take a bootable cd distro (like knoppix), boot from it, mount your /root partition and delete unnecessary files.
If you do not have access to knoppix, just boot from your installation cd and go to the console to do the deletion of files.
I also got into some similar situation and sucessfully solved the problem with help of knoppix
If you need more specific information, just ask.
p.s. Please edit your profile so people can give you an answer that suits to your distribution.