I haven't downloaded it because I'm working on my traditional art, but [link]
was brought to my attention by the wonderful world of Tumblr, so I wanted to toss out there that link. I hear it's easier to use, and is a mix of some of the higher quality programs on the market today. I know there's gimp, but firealpaca might be a good thing to test out if you can't afford to buy a "nicer" program.
(I say "nicer" cause I don't think it's the program that makes the artist, not because I think any one program is better than another. You can buy the world's best art supplies out there, but unless you practice, it's kind of a mute point. Just saying...)