I'd really like to jump in to the source, change a few things, compile, and play my modified version of the game.

But first of all I'm having a hard time compiling it. I'm on Mac OS X and started thinking maybe the problem is that it compiles most easily on Windows or Linux? Google isn't helping much in this regard.

Secondly, where would someone find free (legal) data files to use in place of the official ones that only come with buying the game? Is it easiest to just buy it on eBay, or are there places to find community-made data files?

If this is an off-topic question, please let me know and I'll delete it. I try to use my best judgment on this, but I don't always get it right. And I'm not sure about this question.