I've got a bit of a weird keyboard setup - I have a PC kinesis classic keyboard hooked up to Mac through a Y-mouse PS/2 to USB adapter.
Anyway - the keyboard mappings on Windows keyboards and Mac keyboards are totally different. Namely there's no such thing as 'Alt' or 'Windows' key on Mac and Windows doesn't have 'Option' or 'Command'.
Here's something I found to remap the alt/ctrl keys to be much nicer to work with. If you're one of those poor shmoes that has to work under Windows and you have a kinesis - this is probably useful for you too since you don't normally get the windows key on the Kinesis.