Here’s a great step by step guide to installing the new Apple Magic Trackpad on a normal Windows PC (ie not bootcamp’d mac)…
Step 1: Download the update from Apple (http://support.apple.com/kb/HT4273) It’s an executable file but it won’t run on your Windows Desktop since it is intended only for users who are running Windows inside a Mac desktop using Boot Camp.
Step 2. Download a copy of 7-zip (http://www.7-zip.org/download.html) and extract the contents of the exe file that you’ve downloaded in the previous step.
Step 3. This will create a new file called BootCampUpdate32.msp (or 64 if you’re using the 64bit version) extract the contents of this file as well using 7-zip again.
Step 4. You’ll now have several sub-folders that are named like BootCamp3135*. One of these folders will have a file called Binary.AppleWirelessTrackpad_Bin, just add a .exe extension to this file and then double-click to run it.
via labnol.org