I have seen a lot of questions on how to do this on a mac for testing purposes. Activity Monitor’s CPU pane is nice, but if you want a bigger picture of what’s going on inside your Mac’s CPU, navigate to /Library/Application Support/HWPrefs and launch the CPUPalette program. (If you don’t find it there, insert your Leopard install disc, click on Optional Installs, select Packages, and double-click on CHUD.pkg; that will install CPUPalette.) It will display two graphs showing how busy your CPU’s cores are, and let you disable one or more of them.

