New gaming rig-I'm not sure about nothing yet.

There's no QX6600, only QX6700, QX6800, and QX6850. I think you meant the Q6600.

Get the following:

GA-P35-DS3R

(One of the best mobos out there, and very affordable too)

PC Power & Cooling Silencer 610W

(you can get either a 700W cheap PSU that won't have enough juice for your system and will fry it in a few months like an Ultra or Rosewill, or get a nice, stable PCP&C)

Crucial Ballistix 2GB DDR2 1066

(According to what I've been reading the new G0 stepping OC's like crazy and if you ever have plans for OC'ing it, this is the ram to get. If not, then get Crucial Ballistix DDR2 800)

500GB Seagate Barracuda 7.2k rpm with either 8mb or 16mb cache

(Doesn't matter that much the cache)

eVGA 8800GTX 768MB

(why buy an OC'ed version when you can do it yourself?)

E6850 or Q6600

(Both retailing at $270, the question you need to ask is how often you plan to upgrade and how far are you willing to overclock, if you are willing at all. If you want mad OCs and willing to upgrade when quad cores become a need then get the E6850, if you plan mild or no OCs and you don't want to upgrade CPU anytime soon, then Q6600.)

Total is about $1350 from newegg.com

The thing about the HD2900XT is that if I buy a damn $400 card I expect to see some serious high settings and especially AA & HDR working well. But the HD2900XT performance is killed by AA, so no extra eye candy if you buy this. And even though some people have hope that drivers may fix this, I've been reading too much about how this is hardware issue and cannot be fixed, I rather not even risk it trusting AMD on it, since lately they have been less than spectacular on getting their act together.

It's an pretty decent unit, OCZ makes pretty good stuff, but I just prefer PC Power & Cooling and Seasonic. Just like how I prefer Gigabyte motherboards over ASUS, both make quality stuff, BUT I prefer Gigabyte over ASUS.

CPU: Get the E6600 as those 1333 fsb processers are not faster than the Core 2's, save some money there.
GFX: I'd go for the 8800 GTS 640MB. At NewEgg you can get an 8800 GTX for $500.00
Mobo: The new P35 mobo are the newest chipset that supports Intel's new processers in 2008. $215.00
Ram: Crucial's Ballistix can do 3-3-3-8 @800MHz @2.2volts or 5-5-5-15 @1200MHz 2.2volts. I have two pair that do those specs above. $159.99
HDD: Raptors are the fastest but also very pricey, you can save some money here and get a midend Western Digital HDD.
PSU: Get the Enermax 720 Watt PSU with PCI-Express 2.0 spec'ed for $219.99
PC case: If you don't have a PC case already I'd get a Antec 900 for just over a $100.00
Good luck on your build.