Processor: AMD Athlon 64 X2 3800+ (isn't that AMD's version of the Celeron?)
Mainboard: ASUSTek A8N-E
Memory: It's telling me I have 2 gigs of DDR, but not giving any specific info.
Ok.
There's some good news/bad news here.
Good news: You don't need a CPU fan unless yours is going to explode.
Bad News: Your board is compatible only with DDR RAM, which through an odd quirk of economics is both slower than AND more expensive than the more current DDR-2 standard.
Good news: Your board is on the PCI-E graphics bus standard which means you can upgrade the video card.
You haven't listed what your current video card is, but, and this is important, if you play games, UPGRADING YOUR VIDEO CARD IS THE SINGLE THING THAT WILL BENEFIT YOUR ACTUAL EXPERIENCE THE MOST
It's important. You're not CPU bound in any games with your current setup with the exception of some very intensive sims or the odd strategy game. Your probably not going to see a noticeable increase in performance by adding ram, either honestly. The jump from 1gb to 2gb in XP isn't that big ofd a deal. The jump from 512 to 1gb is huge by comparison. It won't hurt, and might give you a bump in some newer games, it's not nearly as important as the video card.
Think about upgrading that first, and then worry about the other stuff.
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