** EDIT: I messed up this email, and I had to fix it. So if you read an older version, please read this one. It should make more sense. **
kmann1701,
Have you tried booting in safe mode? Start up your machine and hold down the shift key. If you can get to Finder, immediately delete at least a gig of stuff you don't want. Look in /Applications and on your Desktop (as a suggestion).
If you can't start up in safe mode, can you boot in OS 9? Some Power Mac G4s could still boot OS 9. If yours can, hold down the Option key, start the machine, and then select OS 9.
If you have a 9 pin to 9 pin Firewire cable (a good thing to buy for when problems happen), you can connect your Power Mac to a newer Mac. Boot the OTHER Mac. Then hold down the 'T' key on your Power Mac and start it up. Your Power Mac's hard drive will show up as a Firewire drive on the other Mac's desktop. From there you can delete or move files as needed from the Power Mac. This is called Firewire Target Drive mode.
Let us know if those don't work. You shouldn't have to reformat.
Doug