How to switch Cmd and Option keys on non-Mac keyboards
If you've connected a Windows kbd to a Mac, then the order of modifier keys is usually in a different order than on a Mac kbd:
Mac: ctrl, alt, cmd (apple)
Windows: ctrl, cmd ("windows" key), alt
In Mac OS Leopard and later you can go into the System Preferences, open "Keyboard", and first use the "Detect Keyboard" button (if available), then use the "Modifier Keys..." button at the bottom to change the meaning of the modifier keys. E.g, you can then swap the alt and cmd keys so that the order is the same as what you're used to from using a Mac keyboard.
Also, with recent OSX version (I'm seeing this on 10.6.7), you can even set these modifier mapping per keyboard separately so that you can keep the original setting to your std Mac keyboard and only change them for your Windows kbd.