I have seen a few people complain about artifacts but most had the 865PE chipset. Some of them could get rid of it by turning PAT off or to auto, upping the memory voltage, turning off turbo, or raising the memory timings. It is more then likely a board/memory problem or a combo of them.
The reason I asked is I used to get it on my P4P800 Deluxe (865PE) when it was overclocked and the only way I could get rid of it was to replace the board. Try asking in the forum below. There is also a large thread about artifacts in the 3DM03 cpu tests, etc. on mostly 865PE boards there.