Assuming that you don’t have a Macintosh, and you want to use the Magic Trackpad on a Windows system.  All you need is the Apple Magic Trackpad Update 1.0 for Windows, from apple’s site, and a copy of 7-zip. Extract the contents of the exe, then extract the contents of the MSP file inside. There is a driver in one folder titled something like “Binary.AppleWirelessTrackpad_Bin”. Add .exe on the end of it, and run it and it will install the driver.