Screen lockup/scrambling, is this a serious problem?

Recently while playing Fallout 3 on my 1520, once in a while my screen all of a sudden scrambles and either starts lagging like crazy or just locks up entirely. What I mean by scrambles is that it gets all pixelly, like green and pink-ish. When I restart my computer everything is fine, and it doesn't happen very often (and usually only after I play for quite some time) but it has gotten me worried that maybe I have a hardware problem, especially since I've heard that the 8600m cards have been known to give troubles. (it's happened with a couple of different drivers, including 180.84 just now)

I bought a Zalman NC2000 a week or so ago, to keep my laptop cool while playing games - and it's been doing a great job, but just a few minutes ago I ran into this problem again while playing Fallout 3 with the cooler on full setting and the laptop didn't even feel hot. Haven't noticed it during other games, but Fallout 3 is the only one I've been playing for lengthy periods of time (well, Team Fortress 2 as well I suppose). Oh, and if I can get out of the game when this happens the screen usually stays messed up on my desktop as well and I just reboot as soon as possible - but this last time it was just locked up completely and i had to force shutdown.

So I'm just wondering if this is a very serious issue, or if anybody has any idea what the problem may be or any suggestions as what to do? I appreciate any comments or suggestions, because I'm kind of worried.

 

If you are still under warranty you need to have Dell look at this soon. You should be covered by Dell's additional year for the graphics card.