Fishy Space Issues

Hello,

For maybe three or four months my notebook has been giving me the "startup disk is almost full" error several times a day. I routinely delete unneeded files, but this doesn't fix the issue.

I've used programs like The Grand Perspective to delete tremendous amounts of files and programs (I have uninstalled and deleted all the files associated with the Final Cut Suite) and this frees up some space, which is promptly filled without much reason.

I had 20 free gigs on Wednesday morning, left for a camping trip without my computer, and today have only 7 free gigs. I haven't used any programs (besides safari right now) or downloaded anything.

As far as Finder tells me all the files on my hard drive should only add up to about 36 gigs, so I have no idea where the other 470 gigs are that are filling up my computer.

I have read some threads about this but none seem to clarfiy why 470 gigs could just not show up in finder. If there are threads which deal with this comprehensively please refer me to them. Otherwise, if anyone could offer some advice it'd be greatly appreciated.