Noob seeks advice

I'm new to this site and I'm new to building computers, honsestly I havn't got much idea about how to do it. I'm pretty sure I could handle putting the components together, but I'd want to ask, what should I know before purchasing components?

So far I gather I need: A motherboard, CPU, PSU, RAM, GPU, HDD, DVD RW, sound card.

Is that all I need inside the box? (besides the OS ofc)

Before I ask a few questions I should say that my budget on building this new PC is 800-1000£ max (thats 1300-1600 USD), anyway here I go:

How do I configure the USB slots?
What are reliable brands for components?
How big a PSU do I need?*
What are some good CPUs that are comming out soon?
How big of a cooling unit will I need?
What's a good PC tower? I've heard the Antec 900 is good but it seems pretty old, is it still one of the best, cooling wise?
Do I really need more then 4GB of RAM? I've never seen my current pc use more then 2 when running games/media app's


*I'm getting a high end gpu (I'm waiting for the 300 series to come out but I'm looking for something on the level of a GTX 295), as for the CPU, It'll deffinatly needs to be powerful too.

Thanks very much for reading, I'd appreciate any advice/help I can get.



EDIT: How does SLi work? do I need to buy those specifically or can I just stick 2 together via some slot in the gpu? Are there compatibility issues?

And does RPM on a HDD affect life time? They seem cheap enough for me to be able to replace every 2-3 yrs if its that short. 7200 rpm is reasonable?