oh man, that artifacting brings back memories of my 7900GTX. it lasted a few years before any problems, but at the end it just got too bad to carry on. there was even artifacting during internet browsing and normal desktop use (random lines everywhere on the screen).
from what I learned afterwards, it was supposedly a vram issue and nothing could be done (or if something could, it wasn't worth the price).
at least you're still under warranty!