MacBook Pro :: Disk Space Just Going Down?

I always seem to be losing disk space.  Now it is silly, I am not adding any files to the computer but it just goes down.  I have purged all cache files for lightroom, photoshop, final cut render files deleted.  I restart my laptop and note the disk space, say 2 gb left, then an hour later i get the pop message no disk space left and check my Mac HD and it says 230MB or even Zero.  I delete a few files, empty trash, restart machine and it does the same thing again. 

I recently updated to os x 10.6.8 and on updating got an extra 30gb or so which has just been eaten up without really adding much in the way of files that would take this space, so something is just taking the space, i feel it is some kind of virus as such as it goes so quick and without downloading any files that are large. 

Is there something I can do as I am trying to run my mac with no space.  The problem with deleting things are is that it seems to just keep automatically losing disk space so it is a vicious cycle.  

Info:
Final Cut Pro 7