Hi, and welcome to the Geeks to Go forums
(That said, I'm brand new myself!
Looking at your post on the MaximumPC forums, you seem to be very serious about gaming performance. If you intend on building a PC capable of handling the latest games at good resolutions and smooth frame rates, expect to shell out $1000 at the very minimum
. At the time I built my system, it cost me around $1200 and it runs FarCry smoothly at 1280x1024 resolution and maximum graphic settings. I consider my system specs adequate for my personal gaming needs. You probably won't have to pay as much as I did, since you plan on reusing some parts. However, I'd still suggest you get another 512 MB of RAM to bring your total RAM up to 1 GB. (Make sure the speed of the RAM you buy is equal to that of what you currently have.) Also, I think an Athlon 3500+ is a little overkill for you -- anything above an Athlon 2600+ will suit your needs just fine. Get a video card with 256 MB of memory, and you should be pretty much all set for rock-solid gaming stability (as far as the hardware quality goes) and relatively high-end performance.
Your CPU link is pointing to a motherboard, and your video card link to a CPU, so I can't tell what video card you have in mind. Hope this helps.