Download Aquamark 3
HERE this is a 3d Benchmarking program and install and run it - stay in front of the computer as it runs and see if there are any traces of artifacting.
Also download and install 3DMark 06
HERE and run that.
They should both offer an evaluation/free trial of both. The developers of Aquamark3 no longer exist as a company anyways.
These should both push your video card to it's max. If you're experiencing artifacting in these, then in my opinion there is some sort of hardware problem, either (most likely) with the video card itself, or the power supply not supplying enough power (did you also make sure the vents on the power supply aren't coated in dust?)
For S&G's I'd download a demo of the latest game and try playing that too: