There's a slight risk that you could overheat your GPU, as long as you don't push the card too much, you should be fine. If you're uncomfortable, you could get a couple of cooling fans.
you probably need a new build since the pentium d 920's are quite old and getting a E5200 would be good as it doesn't cost much and also you might want to get a 9800 GT which is also reasonably priced