For a hard drive I recommend
250 gb seagate
Or this one if you want to save some money
160 gb seagate
I don't think you will be doing anything that takes advantage of dual core, I'd recommend
athlon 64 3700+
Ram is pretty much all the same, unless you are planning on overclocking, then you need high quality ram.
I'd recommend going to something like tech-forums.net, they can help you build what you want if you give them a budget and tell them what you will be using if for.