Heres an idea....
You could make a folder in the root of your hd and copy all other junk to it.
After that, you can say rm -r to any directory except the backup. After that, install
something else and put backups in there place.
IMPORTANT! If you do this... Make sure whatever you're installing DOESN'T mkfs to the disc!
Like on Slackware there's that option to "Don't format this partition".
Very very very important.