I use a magic mouse at work with a Lenovo X200 laptop running W7. As far as I remember, I did not install extra drivers... just attached it as a BT device.
I did install a utility to reverse the scrolling in windows. It driving me nuts to have my windows machines scroll the opposite direction of my Macs once Lion was released. I knew I could set both directions in Lion... but I liked the new scrolling better. I googled a solution to have W7 scroll the same as Lion.
/Jim