Assuming you don't have the disc for the version you're currently running, you should be able to boot from the 8.04 disc and copy those files to an external hard drive or flash drive, then reinstall.
If you still cannot access those files from the live CD, in the terminal enter the command
You'll now be in a root shell. Now enter the command
All your old files should be available now. The old installation should show up under the /media/disk directory.
If you can get access to the net (a friend's house or something) and want to try to reinstall what you uninstalled, look at the file '/var/log/apt/term.log'
You may need to be root to view it.
****Also, if you reinstall, I would suggest creating a separate partition solely for documents. It's pretty straightforward, just choose the mount point to be '/home/username/documents'. That way if you ever have to reinstall, you won't need to copy all your files over to another drive or partition.