Installing Ubuntu in already created (but empty) partition

To clarify your original problem...are you saying that during the installation, when it asked you for a username and password (and the full, real name of the user, too), you entered information into those fields, but could not continue with the installation? Or are you saying that you installed and booted into the system, but you are unable to log on?

I am not sure the installation will work any better the second time, but the easiest way for you to proceed would be to remove the partitions you created during the first (failed) installation (but not the Windows Vista partition!), and then install Ubuntu, telling the installer to automatically partition the unpartitioned space.

If you want a more technical answer, then you'll have to provide more information. You say it's telling you that you haven't defined the root files. Do you mean the root *filesystem*? If that is the case, then it is complaining that you did not specify any partition to be mounted as "/". If you don't know what that means, then you should probably have the installer automatically create the partitions for the new Ubuntu system to use.

I entered the information (full name etc.) but I couldn't continue. Yes the mean root filesystem. How do I delete the partitions created for the failed installation and what are they called? I really appreciate your help.

You can delete the partitions created in the first (failed) installation from inside the installer, or from the live CD system. Here are instructions for doing it from the live CD system.

Boot the installation CD, and select Try Ubuntu. Once you have a desktop, go to System > Administration > GParted Partition Editor. Assuming all your partitions are on the same drive, you should see them displayed visually as sections of a horizontal bar (and also listed, with details, as rows of text below that). Your Windows Vista installation is in an NTFS partition, and you may have other NTFS partitions as well (for example, as a backup partition used by your Vista system, or perhaps even an entire backup system put there by your computer's manufacturer, for restoring the original state of your Windows system). You don't want to make any changes to the NTFS partitions, unless you really know what you're doing, since you have already shrunk them down to make room for the Ubuntu system.

To the right of the NTFS partitions, you should see partitions for the Ubuntu system. Typically this consists of an ext4 partition and a linux-swap partition. Remove those, by right-clicking on the rows in the list that represent them and clicking Delete. If these partitions were inside an extended partition which is now empty (i.e. they were the only things in the extended partition, none of the NTFS partitions from your Windows Vista system are in it), then go ahead and remove the extended partition as well. Then click the green arrow, to actually apply these operations.

Just make sure not to touch any NTFS partitions, or you can mess up or destroy your Windows Vista system accidentally!

Finally, quit GParted and double-click on the Install Ubuntu icon. Have the installer automatically partition the unpartitioned space for the new Ubuntu system.

I'm not sure exactly what you did the first time you installed, so I don't know if there's any reason to believe that following these instructions would address whatever was causing the installation to be unable to proceed from the step where you enter user information. If you experience that problem again, please let me know.

If you do experience the name/username/password problem again, then you might try installing Ubuntu from the Alternate Install CD. That's a different installer--if the problem is due to a bug in Ubiquity (the installer on the Ubuntu Desktop Install CD), perhaps that would be an effective workaround.

Username/password bug: Make sure that your username begins with a lower-case letter, and contains only lower-case letters, digits, hyphens (-) or underscores (_). Upper-case letters and spaces, in particular, are not allowed. (Of course, the full name can be whatever you like.)

A while back, I fixed the installer for Ubuntu 11.04 to warn about this properly.

@ Colin. That was probably the reason the first time I tried to install. My username began with an uppercase letter. Thanks a lot.

@ Eliah. I used Gparted and deleted an ext4 partition and a swap-partition. They were both part of an extended partition but it also contained a fat32 with Mediadirect (a product from dell) so I didn't delete it. I tried to do the installation again but when assigning space (the easy way) it doesn't seem to accepts the 47 GB of free space in the extended partition and instead it suggests to divide my Vista partition between Vista and Ubuntu. If I enter the advanced options I can see the 47 GB of free space but I don't really know how to use the advanced tool. Is there a way to make Ubuntu take the free space? If not, can you explain to me how to use the advanced tool? I can't thank you enough, all these partitions really confuse me.

If you want to use advanced tools, you must at least make:
  a partition of type Swap of size of your RAM or at least 2GB
  a partition of type Ext4 with remaining space, which will be mounted on /
A better partition scheme is to divide Ext4 partition in two:
  first on of 10GB mounted on /
  second on remaining space mounted on /home
It will make future installation more easy and reliable.

The installation was succesfull. Thanks a lot!