"1. Download this archive and install the filter driver (libusb-win32-filter-bin-0.1.10.1.exe).
2. Unpack ps3sixaxis_en.exe
3. Plug the SIXAXIS into your PC.
4. Run ps3sixaxis_en.exe once.
5. Push the PS button on the SIXAXIS once if it doesn’t see it straight away.
Unfortunately, the motion sensing features aren’t possible on the PC (not yet as least). But still, this is pretty easy way to net yourself a free usable game pad."
Info from gamefront.com