Seems like a modification to SixAxis driver developed by wraggster makes your PC recognize the PS3 controller. It works as USB HID but you should be on Windows XP SP2 or higher OS and 32bit OS is recommended as it may not work well with 64bit OS.
How to Use PS3 Controller on PC
Download and install the filter driver (libusb-win32-filter-bin-0.1.10.1.exe).
Plug the controller into your PC.
Push the PS button on the SIXAXIS once if it doesn’t see it straight away.
Motion-Sensing doesn’t work but hey! you can live with that.