Does this happen when you're not playing? Does it show up in both fullscreen and windowed modes? I'd also like to see a dxdiag. Hit Windows key-R, enter "dxdiag" without quotes in the run box, wait for the scan to finish, click "Save all information," and save the .txt file to your desktop. From there, you can upload it to the free filesharing site of your choice (the free version of pastebin.com is fine) and link to it here.
It kind of looks like we can attach files to posts now, but I'm not sure whether that forum feature is working.