Do you really need the BlueTooth support? I hear the drivers are MS specific and may not work with other BlueTooth enabled machines. Also, it adds cost.
You can get a wireless RF based setup for less money. It comes with a transmitter that plugs into the USB port. I have the MS Wireless Optical Desktop, which works beautifully with my XP machine and my Mac. (AFAIK, the BlueTooth setup will not work at all with the Mac.) I didn't get the natural keyboard version because I don't like the feel of the altered keyboard, but the wireless natural keyboard version is widely available if you want it.