Ok, I just got my Magic Trackpad today. I have it working on both a 64-bit Windows 7 laptop and a 32-bit Windows XP netbook. Here's a quick how-to:
1. Download and install the appropriate driver below:
64-bit:
http://www.megaupload.com/?d=9PG0SLU3
32-bit:
http://www.megaupload.com/?d=EVISIOGI
2. Turn on your bluetooth adapter
3. Right click on the bluetooth tray icon and choose "add a bluetooth device"
3. Press the power button on the Magic Trackpad o it is aiscoverable by your computer. On my XP netbook I had to fiddle around with it a bit before the bluetooth wizard finally picked it up. Double click on "Apple Wireless Trackpad" once its discovered.
4. Use the pairing code "0000" to pair to the device. For XP you should have chosen to pair with the passkey found in the documentation (and filling 0000 in the blank).
Once the device has successfully paired, Windows should automatically use the driver that you installed first. This driver allows tap-to-click, two-finger tap right clicks, two-finger scrolling, as well as the normal physical click. It also allows you to double tap to drag-and-drop. As of yet, I haven't found a way to customize the interface (i.e. disabling tap-to-click or drag-and-drop, etc.). If someone finds how you could do that, please make a post.
If you want the scrolling to look really nice make sure you enable smooth scrolling in your internet browser. In Firefox it's a check box in advanced settings.
BTW, I'm typing on my Apple bluetooth keyboard and using my Magic Trackpad with my XP netbook right now. It works great!