You'd be better off just waiting a while and saving nickels and dimes and building a cheapo AMD rig, since you can get one of their processors for like 60 bucks now. I'm sorry to say I don't think there's much anything you can do with that dell. Maybe try and sell it? Even if you could upgrade the PSU, you'd have a mess of a case, or not case, whatever that thing is.
1: Your PSU is weak and not upgradable.
2. PCI video cards are very poor.
Save your money and build a system. One with AGP or PCI-E, then you could upgrade in the future without any trouble. And DONT buy a Dell.
__________________ Intel Core 2 Duo E6600 @ 3400Mhz
Asus P5B-E
BFG 8800GTX OC
Samsung 400 GB Sata II
Corsair XMS2 2GB DDR2 800 5-5-5-12
Zalman CNPS-9700 LED
Antec Nine Hundred
Hp W2207 22" Widescreen Monitor
Windows Vista Home Premium
Silverstone ST60F 600W PSU
Razer Copperhead Tempest Blue Gaming Mouse