From what I understand the Dell psu's are underrated and if you don't overclock or add additional peripherals the 30amp 12v rail on that thing can power a 9800 gtx with ample head room. Don't go adding any higher cpu though, you'll want to keep you total system draw around 200-250 watts at full load. The rating system on dell psu's reflects actual constant wattage available, if it say 350w then much like shuttle psu's you get 350w out of it. Unlike consumer psu's dells rating is for part specification not to make sales. But give yourself the 100 watt head room and make sure that your 30 amp rail gives you ample head room, I believe a 9800 will draw 9-12 amps. People also run 4850s too.
Warning this is not a guide to a consumer PSU. Just Dell's and shuttles.
Anyone who is suspect of this should be aware that the the 12v rail on this is ample and provides 300 watts constant on the rail alone.