|This definitely sounds like vertex artifacts, which can happen if you overclock a video card - OR if you have a video card that has a problem with one of the cores.|
To test this, I'd suggest finding something that can either record, or take a screenshot, of the game - fraps can work, but you might be able to find something simpler to take a screenshot (Some games have screenshot capabilities built-in). Then you can see if the artifacts show up in the screenshot as well. That will indicate that it's a video card problem instead of a monitor issue.
You can also run furmark and other video testing that will stress your video card and tell if you're getting artifacts after a certain amount of time. If so, the best thing to do is RMA your video card and get a new one - if you haven't overclocked it it should not be acting like that.