Based on the motherboard, i'm guessing your running an Inspiron 545. Dell's website states the installed PSU is a 300Watt. I think if you are able to bump that up to a 600+. You should be able to run that 9800GT. Also, check with your motherboard too about disabling the on-board video GMA (Piece of Crap) adapter. Some require a BIOS setting, jumper or just the existance of a video board in the PCI 16x slot will do it...
(If Intel can make an awesome processor, why can't they make a half decent video card!?!?!?!?!?!)
if u mean bump the PSU up to a 600watt then im sure thats wrong. he will only need like a 500watt.(correct me if im wrong). i have a XFX 4890(uses way more power than a 9800) and a 520watt PSU and it runs fine.