I've been using this recently with great success in Win7 x64.. setting it up is a bit of a biatch.. you need a USB bluetooth dongle or to be prepared to do away with your bluetooth support in favour of a Wireless PS3 controller - you can't have both without a dongle, it takes over the bluetooth radio you point it at. You will also need a USB <> Mini USB cable, like what's used to charge a lot of phones via USB.. this must be connected when you want to charge the controller and when you pair it with your PC - and it isn't included when you buy a controller separately. If you currently have bluetooth support on your desktop PC via a dongle, you'll need a second one -- that's how I'm set up, with both front ports occupied by cute miniusb BT dongles with different coloured lights.
http://www.motioninjoy.com/ (it's free)
I don't even own a Playstation 3 - but since wearing out my Logitech Rumblepad 2 wireless and discovering they don't make them any more, this is the next best option.