help needed for newbie installing ubuntu alongside windows

You have already 4 partitions on your harddrive
unfortunately, it's forbidden to have more than 4 primary partitions... So ubuntu can't create its own partition.

However, there is a way to create more than 4: you create an extended partition which can contains as many partitions as you want.

In your case, you will need to delete one partition first to be able to create the extended one...
Do you have anything in your two 500Gb partitions? The third one is maybe Windows 7. The fourth one, I don't know... You also have Vista, are you using it? We need to find one partition that you don't use or which is empty.

It's a fairly new pc so I would guess that the fourth partition is empty.

But "I would guess" is not enough, I would hate to accidentaly delete your data :)

If you run the LiveCD, choose "try Ubuntu", and check what you have in "Places", do you see the two 500Gb partitions? Can you check what is inside ? The first two ones, I think it's Windows Seven. But then, the two big ones... If they are really empty, tell me, we are going to delete one of them. This will make the installer work much better ;)

When I click on 'Places' it shows: Computer, System Reserved, Acer, Data. If I click on Computer it shows: 1.0 TB Hard Disk: Acer, 1.0 TB Hard Disk: Data, 1.0 TB Hard Disk: System Reserved. The total size of my hard drive is 1.0 TB. Is that of any help?

Ok, click on each one "computer", "system reserved", "acer", "data", and see what files you have in those places. This way we will know which one is empty and can be used for ubuntu. I want to avoid choosing the wrong one and messing up with your computer :)

That's interesting. When I click on each of those nothing happens. Perhaps they are protected?

When I look a the 'Prepare Partitions' screen on the installation process, it gives the following:
/dev/sda1 - size 14680 MB - used 9809 MB
/dev/sda2 - 104 MB - used 35 MB
/dev/sda3 - 492706 MB - used 48165 MB
/dev/sda4 - 492710 MB - used 3221 MB

Mmmm. They could be encrypted maybe... But seems unlikely.
Anyway, your last message gives us some info:

there are just 3MB of files in the last partition. It cannot be Windows 7. And if it's a fresh install, you probably didn't put anything on this partition, right?

In System>Administration, open "Gparted", look for this /dev/sda4 partition (it should appear at the end of your harddrive), and delete it (right click on it, you should have an option to remove it). Then click on the "apply" icon. You will now have 500 GB available.

I don't know how you plan to share your space on the harddrive for Ubuntu.
Windows 7 will NOT see the Ubuntu partitions, so maybe you don't want to give 500GB to ubuntu ? Ubuntu should see the Windows partitions, providing they are not encrypted. So it's up to you, what would you like? If you are ok for 500GB for Ubuntu, you can run the install after deleting the partition.

If you want to give less space to ubuntu and leave more shared space between the two systems, we need to create another partition before running the installer.

Oups, wait, 3221MB, it means 3GB.... Maybe there are files you put there?

It must be the "Data" partition in Windows. If you start Windows 7, what do you see in this partition ?

Boot on Ubuntu CD, and choose option "Try but don't install", then Applications->Accessories->Terminal.
Post result of commands:
   sudo parted -l
   sudo fdisk -l
where "-l" is lower case "-L".
Both commands provide similar results, but exactly the same. And as situation is confused, I prefer to get all data I can.

I have restarted Windows and clicked on Computer/Data(D:). There are a number of small files, a mixture of eula text files, a 'globdata' configuration file, an application installation file (835 KB), and then a number of install.res.***.dll files, and a VC_RED cabinet file (1,883 KB).

Mmmm, something like :

install.exe
install.res.1028.dll
install.res.1031.dll
install.res.1033.dll
install.res.1036.dll
install.res.1040.dll
install.res.1041.dll
install.res.1042.dll
install.res.2052.dll
install.res.3082.dll
vcredist.bmp
globdata.ini
install.ini
eula.1028.txt
eula.1031.txt
eula.1033.txt
eula.1036.txt
eula.1040.txt
eula.1041.txt
eula.1042.txt
eula.2052.txt
eula.3082.txt
vc_redist.msi
vc_redist.cab ?

You've got it. That's what it is showing.

Microsoft says it's not important :)

So we can delete this partition (/dev/sda4)

Do you want to give the 500GB to Ubuntu, or leave some for both Windows and Ubuntu?

For 'delance'. Thank you for joining in with Francois. The report after running sudo parted -l gives the same result as above on each of the partitions, i.e. the sizes are the same.

Thank you Francois. I think that I would like to allocate less than the 500GB to Ubuntu, what about say 100 GB?

Ubuntu is not windows 7, it doesn't require a lot... I would put maybe 40GB, no need for more.

To do that, use the CD to try Ubuntu, open Gparted again and do this:

-delete the fourth partition (/dev/sda4). Right click on it, there must be an option to delete the partition. Be careful, don't delete another partition :)
-you should have a grey area where this partition was before.
-right click on it, then choose "new". Select the option "Extended partition", and click "add". This will create an extended partition that can contain as many new partitions as you want.
-now the grey area is contained in this new partition.
-right click on it again, "new", create a partition with all but 40GB (move the right limit to the left to resize it), with filesystem "NTFS". Name it "Data" in the label field. That will be the partition shared between both systems.

So now you should have the big partition instead of the grey area, containing a new partition, and a small grey area.
Click on the "apply" button, this will create this new partition schema on your harddrive.

Then once it's done, you have now 40GB of free space for Ubuntu, and you can use the CD to run the installer. It will propose you to use this free space.

I know it's a bit complicated, but the way your harddrive is used now is clearly not "user-friendly" to add another system...
If you have any doubt, ask me, dont mess with your partitions. You can contact me on MSN/Gtalk if you want a faster answer, my IDs are on my Launchpad profile page.

Francois, thank you very much indeed! I now have Ubuntu and Windows installed. I am very grateful to you.

I am not sure, however, if my partitions are correct. Can I ask you to just look at the following to see if I have followed your instructions correctly:
Partition File System Mount Point Label Size Used Unused Flag
unallocated unallocated 1.00 MiB
/dev/sda1 ntfs PQSERVICE 13.67 GiB 9.14 GiB 4.54 GiB
/dev/sda2 ntfs SYSTEM RESERVED100.00 MIb 33.9 MiB 66.41 MiB boot
/dev/sda3 ntfs ACER 250.61 GiB 44.5 GiB 206 GiB
unallocated unallocated 208.26 GiB
/dev/sda4 extended 458.87 GiB
     /dev/sda5 ntfs DATA 39.46 GiB 87.0 MiB 39.37 GiB
     /dev/sda6 ext4 411.48 GiB 11.41 GiB 400.07 GiB
    unallocated unallocated 1.00 MiB
    /dev/sda7 linux-swap 7.92 GiB

Everything is working fine. Thank you once again for your support.

Ok, so from what I see, you have now
-a smaller /dev/sda3, with some space left after it (200GB)
-a 500GB extended partition, including a 40GB Windows partition, a 410GB Uuntu partition and a 8GB Ubuntu swap (the swap is some kind of additional memory in case your computer has no more).

So you can maybe adjust this a bit:

-the 200GB after sda3 are lost, you should resize sda3 to include them again
-you have set 410GB for Ubuntu and only 40GB for the shared Windows partition. That should be the opposite :) I would resize the UBuntu partition to be 40GB only (grab the left border, move it to the right), then resize the Windows one to be 410GB (grab the right border, move it to the right)

You can do all this from the LiveCD & Gparted. You cannot do it from the Ubuntu installed on the harddrive, as you cannot modify a partition which is currently used. So the LiveCD is very useful for this kind of operation.

Remember to save all important documents on an external backup before doing those operations on partitions. It's very reliable but you never know.

I think I have it right now! Thank you once again for your support and guidance. Ubuntu is a great system.

Have fun ! ;)