A good chess engine is hard to find

The free Crafty 21.6 binary for Windows may be downloaded here. You'll need a GUI, either WinBoard 4.2.7 or Arena 1.1, most likely.

Update — Beowulf 2.3 is also free, also interesting and also needs a winboard-style GUI.

WinBoard has been a favorite of mine for years, mainly because it's a Windows version of the old Linux xboard, which hosts GNU Chess.

However, if what you want is a good free Windows chess program, pure and simple, then look at Mayura. The Sjeng engine, included with Mayura, can beat most of you clowns at its default level (expert), but you can dumb it down and beat it handily if you pay a modicum of attention. Another one in this category is NagaSkaki, which can play at the braindead level. I recommend these because they both have clean, pretty interfaces without a lot of chess fanatic clutter, and they can be handicapped against beginners and young children without condescending.