How Do I Roll Back to a Previous Version of a Video Card Driver

My PC is crashing sometimes while watching streaming video. It freezes, then gives me the blue screen, saying something about watchdog.sys. I think that the problem may be the current version of the video driver for my NVidia GeForce 9600 GT video card. I would like to roll back to the previous version of the driver. Hours and hours of Googling the problem have lead me to this conclusion. Reinstalling the same driver doesn't fix the problem. I have the old driver in the NVidia folder, but have no idea how to switch back to it. The rollback feature in My Computer refuses to do it, saying something about no backup. Could someone give me step by step instructions for doing the rollback? Thanks in advance.

Brandon