Few bits for you:
- What motherboard? Try Gigabyte X48 for overclocking and Xfire, or P45 a cheaper alternative. Asus are also making some well regarded boards at the moment.
- If you are overclocking you will want an aftermarket heat sink. There are good ones from Xigmatek (Rifle cooler).
- DDR3 is overpriced and underperforms for the money. Go with DDR2. Probably PC6400 will suffice but check with more knowledgeable people about matching clock speeds. Ideally you want a 1:1 FSB:Memory clock ratio.
- 4Gb of RAM is the right amount to go for, but you will only get all of it if you are using a 64bit operating system.
- What about power supply? Try Corsair, enermax (expensive but quiet) or PC Power and Cooling (Silencer 610W). Something around 500-600W will be ample - probably overkill.
- Also you need to decide on a case + optical drives. Personal preference.
- You could upgrade the graphics card in the future and this is probably the wisest thing to do. NVidia will have to strike back against ATi and this will probably happen as a price war initially. The longer you wait the more the price will fall.
- Rather than going for an X2 card when they are released you could Xfire at a later date.
- Equally the graphic is useless unless attached to a good monitor - Samsung make good ones, Dell 24" are apparently good too. Check the PC Pro A-List for a start and then other forums and reviews.
- Seagate Barracuda 7200.11 would do well for a HDD, there are also good offerings from Western Digital and Samsung. Check the Tom's Hardware hierarchy charts.
- Lastly and possibly most importantly; no PC you build will ever be "future proof". Technology moves on and you get left behind. This system looks good for the next set of games but come 3 months time and the launch of the new Intel CPU's this machine won't compete in the same way.
- In this vein you may wish to think about a quad core CPU. Wisdom would have it that coders will want to make use of the increase use of quad cores to run programs faster. If you want this computer to last for 1 year go with the fastest dual core you can get (higher frequency is best for gaming), but if you want a few years out of the processor you may want to look at a quad.
Hope that is useful.
Jeremy