I'm looking to buy a stereo for my brother's '00 forester for his birthday, but I have no idea what kind to get. I don't want to make him suspicious by digging around in his dashboard, and I couldn't find any helpful information (at least for me) online.

What kind of stereo system can I get that can be installed in his '00 forester?

Try www.crutchfield.com (http://www.crutchfield.com) They should be able to point you in the right direction.