Choosing a proc. and MB for gaming under $600

Hi - I'm trying to follow the sticky here. Let me start off with the background: My Dad is a gamer on a budget. He likes to get the best machine he can for the money and play games like fallout3, Oblivion and Black and White. I built him a PC about 2.5 years ago for around $800 and unfortunately, the Northbridge fan died and killed the machine. He is going to reuse some parts for the time being - but he needs new MB/Proc/Memory.

What I'm wondering if at this point in time - whats the best way to go? I proposed to him 2 routes from globalcomputer.com: a Core 2 Quad 9550 with MB and Ram for $400 or a i7 920 with MB and RAM for $600. He is thinking that in 2 years its going to be outdated and he'll need to upgrade so he'll just go with the socket 775 Quad. I'm wondering if at this point its worth the extra $200 to go with the i7?

So, which way should I go? Or, shoudl I go with an AMD being as I'll see more performance out of a video card improvement?

Thanks for all the help ahead of time! Below is what he has:

APPROXIMATE PURCHASE DATE: Very soon - machine dead BUDGET RANGE: Under $600 at extreme most

SYSTEM USAGE FROM MOST TO LEAST IMPORTANT: Games

PARTS NOT REQUIRED: Keyboard, Mouse, Monitor (22" HD LCD with HDMI and DVI inputs), Case, Optical drive, HD, Floppy, Power supply (Ultra, X-Finity, 500-Watt, SATA Ready), Video card (EVGA GeForce 7950 GT/ 512 MB / SLI / PciE)

PREFERRED WEBSITE(S) FOR PARTS: Globalcomputer or newegg (although - I'll go anywhere if I have too)

PARTS PREFERENCES: None

OVERCLOCKING: No SLI OR CROSSFIRE: Maybe

MONITOR RESOLUTION: AS good as we can afford - Probably highest at monitor max - 1920x1080

ADDITIONAL COMMENTS: I put awesome blue LEDs all through it and he hates them. Of course they are staying!