And if that's all you want CHDK for, you don't need to do much more than install it - usb triggering works pretty much 'out of the box'.
@zeno : thanks for the clarification - perhaps my explanation was going to scare dave.stewart.5621149 away ? That was not my intent.
However, he does need to learn how to find the right version of CHDK for his camera, install it on a configured SD card, setup the USB remote menu items correctly and source a USB remote switch.
@dave.stewart : it does not really say this anywhere, but you can use any USB cable that has the right connector for your camera to test things out. Plug the cable into your camera and then plug and unplug it to/from your PC to simulate pressing a switch. The power from the PC will activate the USB remote code (if its enabled) just like any of the switch devices listed on the wiki page. Not much use unless you are sitting at your PC but a simple and inexpensive way to just test things out.