Need help making couple key decisions

Currently I’m in process of replace my computer of 5 years old, I went through lot of articles and posts and come to the conclusion instead of trying to update my old system I should just starting building a new one.

Like lot of other people before me I had done lot of researches and price comparison, before I narrow down my choices to the following components, I plan to build my system with the idea that it’s upgradable in the future with mid range components, just need you guy to steer me to the right directions =) OC or not it’s okay with me.

CPU I have budget of $200, I can go either Q6600 or E8400 or any suggestions
CPU Cooler I already have Zalman cnps7700
Motherboard MSI P7N SLI Platinum or any good mb, I have $200 budget
RAM I just brought Crucial 2x2bg pc2 6400 for very good price, I just don’t’ know if brand of ram matters.
Graphics 2x XFX Geforce 8800 GT 512mb
Hard Drive Need suggestion
Sound Anything onboard is fine with me
Case I already have Antec 900
Power Thermaltake toughpower cable management 750w or COOLMAX CUG-700B 700W ATX 12V

^^^ Ain't that the truth? If the 2.4Ghz ain't enough in the future, you can overclock it to 3Ghz on stock cooling.

What's the use of the pc?