Need some advice in purchasing a gaming PC

Hey guys, I would just like some advice in choosing between these two PCs. My old one ran poorly and I'm looking to get a decent one for around $1200 or less. Here are two I've found so far that seem decent.

Antec 500W Power Supply SmartPower 2.0

Motherboard
ASUS A8N-E NVIDIA nForce4 Ultra ATX Motherboard for AMD Socket 939 CPU

Processor

AMD Athlon 64 4000+ 2.4GHz 1MB L2 Cache Socket 939

Memory

Quantity 2 of Corsair XMS Extreme 1GB (2 x512MB DDR400 Timing 2-3-3-6 (Total 2GB)
or
CORSAIR XMS 2GB (2 X 1GB) DDR 400 TIMING 3-3-3-8[-$11.00]

(not sure if the lower timing would be worth the fact that they come in four 512s instead of two 1024? Any input here would be great)

GeForce 7600GT 256MB/128-bit GDDR3 PCI Express x16

Sony 16X DVD-Rom/32XCD-RW Combo Drive



Or I was considering this PC

http://www.tigerdirect.com/applicati...Tab=2&NoMapp=0

I'm just not sure how much better if at all dual core systems are for gaming. They boast superb multitasking ability, but I would figure that would be for people who work with multiple memory intensive programs at the same time. I have no need to play two games at the same time so would dual core even be worth looking into? I thank anyone who responds for any input you can provide.

Jam it back in, in the dark.

Thanks for the input guys I really appreciate it

There's nowhere I can't reach.