Here's an old piece of chess software, and yes it works under XP, though I'm not sure if it'll work under Vista or Windows 7. Chess System Tal II is a chess game and sequel to Chess System Tal. Different from most Chess games but similar as its predecessor, Tal doesn't try to play the best and most safe move every time, but instead it has its own personality based on professional chess player Mikhail Tal, who's known for making unexpected moves and having an attacking play style. You can play the game from various perspective including top-down with iconic display and 3D from the player's perspective. Published by Oxford Softworks. You can download it here (RAR archive, 30 megs).
(From the NFO) Chess System Tal II is a knowledge based program. It packs many chess ideas into its evaluation function. It helps to give it some time to work up its ideas. The longer the time control the better.
CSTal II is not designed to play fast chess against other programs. It is designed to play CHESS against other chess players (eg humans). You can watch CSTal play, see its ideas, observe the positional and sacrifical algorithms and learn new concepts from it. Playing endless automated games against other materialistic programs is not recommended for the sake of your own sanity and the development of your own brain. Please get a tank of fish instead.
How to install: Unrar it to a subdirectory and run the CHESSTAL exe, nothing needs to be installed.
There's also a new UCI Chess engine called Stockfish, here is the link. Why do I mention Stockfish? According to GM Lubomir Kavalek (from his Huffington Post column): In a recent computer tournament, ran by Martin Thoresen in Norway, Rybka 4 lost to a program with another fish name, the Stockfish. The name suggests a dead fish, but in this game it came wonderfully alive. It was a typical Grunfeld Indian game, a classic confrontation between a strong pawn center and active piece play with a romantic aura that would have pleased players from 19th century. It is a chaotic masterpiece in which one king goes for a walk, the other is hunted and the sacrifices range from pawns to queens.