Get the Q6600 processor and save some money. There's not enough difference in rendering time to justify the price. I know from experience. Look at my setup and I am using it for just the same reason, video editing and little gaming.
is there huge difference in speed between Q6600 & QX6850?
Yes, but not enough to justify the huge price difference. An overclocked q6600 can take on a QX6850 stock anyday tho.
4X1gig DDR2 800 ram (any good brand)
A good solid 700W PSU
A P35 board will do fine if no SLI
Thermalright Ultra 120 Extreme for heatsink
Learn how (if you don't) to overclock and get your Q6600 past the QX6850 speeds. I would say what the choice of the motherboard should be, but then again everyone has his or her preference. The 1066mhz ram is overkill, just run the ram in 1:1 ratio and the 800mhz ram should serve you fine.
EDIT: Just read that you don't want to overclock. The Q6600 is still the better value even without overclocking, and 1066mhz ram is now truly overkill.
Get the Q6600; runs at 1066 fsb (or 4x266 quad pumped).
Get 4 gigs PC2-5400 memory; runs at (2x333 - 4:5), is plenty (you technically only need PC2-4300 memory to run 1:1.
P35 and X38 chipsets are good (I like the Asus Maximus Formula).
1000W PSU is overkill but a good power supply is necessary. Quite honestly the Corsair HX620 will be plenty, even the HX520 would be fine (yes, even with a quad).
The 8800 gt is a great card. second card should be nvidia as well.
4 gigs at PC2-5400 is better than 2gigs at PC2-6400, or even 8500. vista 32 will use the 4 gigs.