Did I recommend updating DX and you said you already did? Somebody deleted my post (Whoever deleted my post didn't move it to deleted posts\threads or send a courtesy pm).
I get a crash in blackops after around 2 or 3 rounds or 20 minutes of single player. Generally dxgkrln.dll or a dll with ati in the file name will crash. I found a hotfix for vista\win7 directly relating to dxgkrnl.dll however when I tried to install it it claimed the hotfix did not need applying to my system. I'm not too worried about it, I usually get bored and quit before the game crashes.
I assume you've tried lowering all your ingame settings, changing resolution, changing graphics quality settings in windows tools (ati\nv tools)..etc.. changed AA and AS settings and all those kinds of things?