1. dont get dual 280s, thats a complete waste of money for WoW. A single 280 is more than enough to drive 5 wow windows, if you have more than 2 monitors you can get a cheap 2nd video card

2. Vista 64 bit can see something ridiculous like 4 terabytes of memory. You will be doing great with 8GB of RAM, 4GB is ok but you will be 10x happier with 8GB.

3. Make sure you get Vista64, for a new PC no reason not to as said above.

4. While your CPU/motherboard choice is fine, its pretty much top of the line and you don't "need" that. If something like the Q6600 is hundreds cheaper you may want to look into that. Its a personal choice of course, its just that usually the "very best" in CPU and video cards tends to come at an extremely high premium, and you can save 30-50% if you go down "one step" while only losing 10-20% in performance. A very acceptable tradeoff.

5. remember WOTLK will be more demanding on computer/memory, and Intel/nvidia are releasing new products in a few months as well. Its a constant chicken and egg thing - imo its better to spend a little less now and upgrade sooner, than spend a ton now and try to hold off 2 years on upgrading. No matter what you buy today, one year from now you will be able to buy 2x the power for the same price.