There are a handful of utilites/drivers to use the dualshock 3 with PC. I tried one years ago but it could only be used through USB and disconnected your other USB devices, so I ended up picking up a wireless 360 controller. I think some of the more recent ones work just fine and will also let you connect through bluetooth with a dongle. After that I believe you have to set it up in each game as a third party controller.
It's nice to have most games automatically pick up the 360 controller, but even then some things just don't work right. I think I had to re-reassign some of the buttons in a couple games to get things working right. Camera didn't work right be default in the Assassin's Creed games and some face buttons were swapped in either AC or Prince of Persia. Just hit me while writing this that it may be an Ubisoft thing, because I only had issues with their games, everything else picked up just right.