I wouldn't get the 790i and DDR3 RAM.. there isn't much of a difference between DDR2 and DDR3 at the moment.
A 780i - 750i FTW (3 and 2 way SLI) and OCZ Reapers or Crucial Ballistics is a good pick. - That is ONLY if you wish to go SLI... I would recommend another motherboard if you don't want to go SLI...
Note: The 780i does still have some bugs in it's system.
You do not need 850w of power to run this rig.. I think a 500+ will be plenty... (not SLI)
As far as the CPU goes.. I would pick the Q6600... The Q6700 is a better choice now though because it went down soo much in price and it has 10x multiplier... They both overclock extremely well. Both of these CPUs beat the Q9300 in many tests I have seen.
As far as that GPU goes.. I would wait until August if possible.. (Early - Late Q3 of this year)
Prices should go down a lot as NVIDIA unleashes the beast it's been keeping in the cage behind the puppies...
* For the sound card.. what you have selected includes X-RAM which only helps compared to as 2-3 frames at the most intense situations.. not much at all. The ONLY thing besides X-RAM that the Fatal1ty offers is the SOFTWARE... the software for this card is rocking awesome totally transforming music.. As I say I believe that sound is 70% Software and 30% hardware
Note that some of Creative's products have had problems converting to Vista.. Lets not forget that Vista was really buggy before SP1 and now a ton of these issues have been fixed allowing products, such as this sound card, to better connect with the operating system thus taking out some driver errors...
This card has a lot of potential, though I wouldn't recommend it as a solid device because it does have a few bugs in it's system.
What size monitor will you be using? 22", or bigger..?
Are you going to overclock?