I use motionjoy as well to connect ps3 dual shock via usb cable. So far the games ive played using it is trackmania and dirt2. Like ssddx said, as long as the buttons are mapped properly, the games supporting controllers should have little to no problems as the ps3 controller is treated like a standard controller.
If you go the motionjoy route, remember to restart the computer after loading the driver. This catches many people out wondering why its not working.
Loading driver part i mean after installing motionjoy (ds3 tool) application, under tab Driver Manager, click Load Driver. Then restart computer once its done.
To use the controller, run the application again and under Profile choose the controller and click enable button beside vibration test.
Not sure if autorun in the Motionjoy options on windows startup will enable controller automatically or just start the application, but may need to click enable button before playing games every time the computer is turned back on.
Thank you guys for not being a smart ass with the answers. Though i've been reading alot on some forums and they've been reporting bugs and driver crashes running it with motionjoy, so im not sure at all if i want to try it and have my rig messed up just to use a ps3 controller. But on the other hand, there's success stories where it totally worked for them without giving them any sort of problem.