Apparently fonts can become corrupt - maybe that is the problem. You might try TweakUI XP which is supposed to have a repair font folder option. I'm not sure if it will repair or detect a damaged font of it's only intended to fix problems with the folder itself though.

 http://windowsxp.mvps.org/tweakui.htm

You also might see if you can access the folder in Safe Mode and delete fonts that way. If not, then the command line may be your only option. I'd try making a copy of the folder, delete everythig in the original and then copy back only the ones you really need - no gurantees that won't destroy the world so set a restore point beforehand. 

"Democracy is a pathetic belief in the collective wisdom of individual ignorance." - H. L. Mencken