[Fedora 12] "IOError: [Erno 28] No space left on device"

[compdoc]

As Kevin J. Cummings said, you want to boot to runlevel 1, which is text mode. 
Boot to the command line, in other words.

Google:  fedora 12 runlevel 1

And if you are able to log in as root, you need to look at all of your 
partitions and see which one is full. If you aren't sure what to delete, ask 
the mailing list.

Don't mess with selinux.