Also, was screwing around and it seems that, if you change the following byte in a hex editor, you can cheat and skip to later levels in the game:
Not sure what the exact relationship is here, or if there are other bytes that are related... the screenshot has my config.dat from being on level 18... I changed that to a 48 and had up to level 50 available... must be something else, but you can still probably get a ton of levels by screwing with it.
I'd recommend backing up your existing config.dat before messing with this (just in case it doesn't work right for you)... don't wanna lose all your hard work!