Okay, I have alot to say about this.
There are a lot of reasons to play chess. If you want to get good then there is no substitute for
Fritz 8 -The controls are a little complex for adjusting levels and setting up boards but once you get used to it -you will play at your own level and get REALLY good. I've seen this firsthand in the chessclub that I go to.
Chessmaster is also a good program but not on the level of Fritz. The cool thing about chessmaster is that the computer simulated opponents REALLY seem to make the mistakes that humans make when they play. There are probably a hundred or so computerized opponents of varying degrees of ability. You could get better just playing at your hardest ability level until you finally beat that opponent regularly -then move up.
Chessmaster is easy to learn the controls.
That being said, there are other chess programswhich do the trick if you just want a game. I've played battlechess at my nephew's house. It has cool 3D animation and is definitely fun. There are tons of chess programs out there and I am recommending the two at the top.