Dual core isn't needed for now. But in time, it will be required. Make sure you get a motherboard that will accept a dual core CPU later.DDR2? It actually costs less than DDR, but it really depends upon which way you go - Intel or AMD. If you go AMD, at this point it's best to go Socket 939, and therefore, you should go DDR since S939 mobos use that. If you go Intel, there's no question about it - go DDR2.
For CPU's, don't bother with the Athlon 64 3800. It is simply a higher clocked Venice than the 3000, 3200, or 3500. If you're saving money, look at the 3000 or 3200 because clock speed just doesn't make much of a difference in performance. You'd be better off putting that money on a better video card than the 7600GT if you want to spend it. If you truly want better performance than that CPU, go with a Socket 939 CPU with 1M of cache, such as the Opteron 144, or the Athlon 64 3700. However, I would encourage you to focus more on the video card first.
To illustrate this, take the following example. While the 7600GT is a good card for the money, an Athlon 3000 with a 7800GT or 7900GT would perform far better in most games than an Athlon 64 3700 with a 7600GT. Plus, I would have him plan on upgrading to dual core on his motherboard sometime next year once the prices are low, so why waste money on a better CPU now?
As for the motherboard, DFI makes an Infinity NForce 4 Ultra motherboard for about $100. It does support all S939 dual core processors as well. DFI makes the best quality motherboards for NForce4.
Lastly, Sabertooth is right. If you can wait a few more weeks, you should see both AMD and Intel CPU prices plummet even more than they have already. It would benefit you if you can wait just a bit longer.
"Milk was a bad choice!"
