How do I use Wii remote and other controllers for PC games?

The wiimote can be connected to a computer using BlueTooth. There's a tutorial here on how to connect the wiimote to the computer via a program called BlueSoleil, which is often bundled with BlueTooth sticks (it was bundled with mine). The computer should recognize it as a joystick.

Also, this page lists some interesting things you can do with it. Johnny Lee's project are particularly impressive.

Finally, this page on the WiimoteProject site has a more in-depth guide for various ways to connect it, not only using BlueSoleil.

The Wii remote communicates via Bluetooth, so you'll need a Bluetooth receiver.

The games you want to play will also have to be capable of reading input from a Bluetooth device.

GlovePie is a great tool that can be used to get input from a wii remote and use it in an existing game.