Yeah, don't get 4x512, that is really silly. Get what Freestyler posted or this
which has much better timings but it is 20 bucks more so it is up to you.
Also, for the HD you might want to look at this Seagate.
The one you have now is fine but this hard-drive has thousands of good reviews and slightly better times. I own it and I am always the first into a map while playing CS:S it is a beast.
Edit: Also, I encourage a slight CPU upgrade, maybe E6420 or something, but once again-- it's up to you.