Buying advice for ram

I just got a hold of an E-Machine W3611. Below I listed the specs pulled off E-machines website for my comp. Basically I was looking for some advice on purchasing RAM from a internet site like New Egg or Tiger Direct. I'm halfway computer literate, but I'm a lil slow when it comes to the hardware side. I want to get the full 2 gigs of Ram into it, in hopes I will be able to play Civilization 4 without all the lag, or having to buy a new vid card. Which I will probably be looking to do next, but money is hard to come by for me at the moment, so I'm going to go with RAM first. If anyone has some suggestions on some affordable and compatible ram for my comp there advice would be greatly appreciated. Thanks ahead to anyone willing to spend there time on my novice question. -qball

CPU: Intel® Pentium® 4 Processor 631
Hyper-Threading and Intel® EM64T Technology
(3.00GHz, 2MB L2 cache, 800MHz FSB)

Operating System: Genuine Windows Vista® Home Basic

Chipset: Intel® 945G

Memory: 512MB DDR2 dual-channel capable (1 × 512MB), 533MHz (PC4200)
Expandable to 2GB
2 DDR2 Slots (Total), 1 DDR2 Slot (Available)

Actually has 1014 mb of ram according to device manager, 4 ram slots with 256 mb ram cards in each slot.

Hard Drive: 160GB SATA II (7200rpm, 8MB cache)

Video: Intel® Graphics Media Accelerator 950 <bahhhhhh
Up to 224MB Shared Video Memory
PCI-Express® (PCI-E x16) slot available for upgrade


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