I'm currently running dual 9600GT's in DirectX with no arifact issues theres a few tricks to it though,

1: uninstall your video drivers
2: re-install DirectX 10 via http:\\download.microsoft.com
3: install the latest drivers from nvidia
4: make sure to turn off full screen glow, death glow effect, and vertical sync in each wow and turn on the triangle reducing option

you should be good to go