I would vote for rewriting the thing from scratch. You'll probably spend roughly an equal amount of time whether you rewrite or fix, and if you rewrite you will (almost certainly) end up with better code. Of course, alot of this time will be spent in determining what the program does, and 'breaking it into' smaller pieces as others have suggested, but just think, if its that badly written, I bet you can turn that 4K program into 1K (ok, maybe 2) :)