No matter what I seem to do I get weird "boxy" artifacts appearing on textured surfaces on an ATI 4870 x2. Anybody have any idea what's going on there? It seems like stamps are being replaced by incorrect textures

Yep, your not the only ATI person, ATI cards are having the worst of it. I'm assuming a nice hotfix will fix all the gfx loading problems. hopefully any day now since its a major problem for a lot of players.