My memory on one OS is different than on Ubuntu

It sounds like you installed using Wubi (the windows installer). When you install in this way, you set the 'size' of the installation (the virtual disk) and that size is fixed - it won't dynamically resize itself. 3 GB sounds very low for the root.disk - I think that is the minimum install size, but it doesn't allow you to do much.

If you partitioned your hard drive and installed Ubuntu direct, it will use whatever size partition you gave it. Again it's up to you how much to give the ubuntu partition and you can't borrow more from another partition without resizing.

If you want a definitive answer, post back the results of "sudo fdisk -l" (that's a lower-case L) and also "df -h". You can run these commands in a Terminal window (click on Applications, Accessories, Terminal). For the first command you need to reenter your password as it requires elevated permission.

When I typed in sudo fdisk -l it gave me

Disk /dev/sda: 160.0 GB, 160041885696 bytes
255 heads, 63 sectors/track, 19457 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0xc2b57a73

   Device Boot Start End Blocks Id System
/dev/sda1 1 1275 10240000 27 Unknown
/dev/sda2 * 1275 19458 146048000 7 HPFS/NTFS

and when I did df -h it gave me

Filesystem Size Used Avail Use% Mounted on
/dev/loop0 11G 5.9G 4.0G 61% /
none 370M 280K 370M 1% /dev
none 375M 2.0M 373M 1% /dev/shm
none 375M 88K 375M 1% /var/run
none 375M 0 375M 0% /var/lock
none 375M 0 375M 0% /lib/init/rw
/dev/sda2 140G 101G 39G 73% /host
/dev/sr0 466M 466M 0 100% /media/FVDES0910DVDR7

OK you installed using WUBI (installed from windows) and you set the virtual disk install size to be 11GB. You have 4GB of space remaining on this disk. Your /host directory (your windows partition) has 39GB free.

The size of the virtual disk is fixed (you can see it as it's a physical file under windows c:\ubuntu\disks\root.disk). Ubuntu won't use any of that 39GB automatically, although you could manually move some data over to it.

Your options are:
1. Reinstall Ubuntu with WUBI making the root.disk larger (NOTE: reinstalling will delete your current wubi install and everything on it so backup first). This is a good option if you haven't done much tweaking or stored any personal data on Ubuntu yet.

2. Resize the root.disk - there isn't currently an automated procedure that works on the current version, although it's possible to do this manually (don't use LVPM - it won't work with current versions - or rather it works with workarounds).

3. Migrate your /home directory to a new virtual disk. The wubi guide has a script that can do this: https://wiki.ubuntu.com/WubiGuide (see "How do I resize the virtual disks?" and look for the part about moving /home to a dedicated virtual disk). Since most data is stored under /home this might be a solution.

4. Use the Vista disk utility to create a new dedicated partition and install Ubuntu into that or migrate your existing wubi to it (keeping your current settings and data): http://ubuntuforums.org/showthread.php?t=1519354

Before you try the any of the above, it's a good idea to take a straight backup of the root.disk file and place the copy outside the \ubuntu directory. Then, if things go pear shaped you can recover your entire Wubi install and the data in it. Obviously it's big, so you might want to put it on an external drive (otherwise it takes up a chunk of your 39GB remaining). It's a good idea to backup all your data anyway, especially if you are partitioning or installing a new OS.

I will just reinstall Ubuntu I guess, its pretty new and nothing big is on it. Thanks for all you help :D.