Hey Sock...

Don't know if you got your probs sorted, but I've had similar issues...

What graphic card U got ?

got the latest drivers 4 it ? (They release drivers every couple of weeks simetimes on new hardware)

If that doesn't help, try backing off your graphic settings a little, go down one resoloution or back off the detail a little, you get the idea...

Keep backing it off until its stable... I know this may be a pain if you have a posh new graphic card, but there will likely be an update in the near future if that's the cause..  If it's an older card it may just be that your pushing it too hard and it just won't be stable at that speed, in which case backing it off should cure it too..

Reinstalling DirectX 9.0b is a LAST resort only if all else fails... I don't think it will help really, but if nothing else worked I can't think of anything else to try short of a clean install of your Operating System.. so try DX9b before you try reinstalling the O.S. I know it's a pain, I bin there, but it will cure the problem.

Good Luck !