winxp 64bit: not good driver support for most things out there. you won't be able to run much. most ppl just use 32bit windows on their 64bit machines.
dual core amd processor: sounds like a great idea! if you want to overclock, the best deal right now is the opteron 165 denmark. if you don't want to overclock then 4400+ or 4800+ will be good enough. if you're TOTALLY loaded, then why not hit up an FX-60 (not very good performance/price ratio..since its very pricey)
ram: 2X1gb is good. if you plan on overclocking look into getting ram that is higher clocked (e.g. ddr500) just incase the ram you pick doesn't overclock.. if you're not gonna OC then just look at timiings.. gskill and ocz are my brands of prefrence. (corsair tends to be overpriced IMO.. but lots of ppl here love em.. )
raid 0 : sure, why not! hehe.. couple of raptors in raid 0. and a big HD for big file storage.
SLI: you get 20-50% increase by paying an extra 100%. waste of money. only if you have a lot of money to blow.. (if you get the fx-60 you'll probably want this too, hehe). top cards now are the 7900gtx from nvidia, and x1900xtx from ati. ati's version of SLI is called crossfire, but since its newer it isn't as efficient... (not like SLI is efficient or anything..)
soundcard: the X-FI is what ppl swear by hear.. by i don't think it has optical out... that would probably be what you should be looking for..
so whats your budget? maybe we can help you out.
i'm not sure if physics cards have been relseased yet...
"Is virtue a thing remote? I wish to be virtuous, and lo! Virtue is at hand." -Confucius