Yeah, ultimately, I would consider gaining some knowledge of the theory and compositional skills that are required to score for video games. The only way i've been doing it, is because I have buddies in programming school who request me to do music for them. Most of the time however, I just work on student comissions; it's all about networking. But if it's just for fun, go all out, as much as you want. As for what you want to buy, you need to specify genre probably. Like if you wanted to do electronica, I've had a lot of success with Digital Performer 6 (Mac only) in the studio I work out of, though I make musique concrete most of the time while I am in there. I've found that the Macs provide me with more programs to work with in my experience.