GIGABYTE GV-N66T128D geforce 6600 128 meg agp 8x Video Card help

i googled but i couldnt find anything answer, so maybe people on kirupa can help me. i just bought a geforce 6600 128 meg agp 8x GIGABYTGV-N66T128D Video Card, i installed all the drivers and etc. i ran counter strike 1.6 and it ran perfectly. than i tried to run cs source, when i tried to get in a server or make a new game, everything goes haywire and you will see like lots and lots different colors of spots, weird.