New $1400 rig - please give your thoughts. Thanks!

I hear that some people have been lucky and have gotten the GO stepping on the Q6600. Maybe you could call and see if they have the Q6600 w/spec SLACR This is the GO stepping.

You will need DDR3 memory if you plan to use the P5K3 ASUS mobo.
If you use the DDR2 memory then either the P5k Deluxe with Wi-Fi or the P5K without Wi-Fi.
If you want to save alittle on the GPU get the 320Mb there is not much difference in frames between the two cards according to THG charts. If you are going to buy the 640Mb then spend alittle more and get a GTX card instead. Big jump in frames going to GTX card.
Can't help you on the Sound I'm not an audiofile(sp?) I just use what is on the mobo.
I dont duel boot but plan on it the next build I do in a couple of months. Plan on running Ubuntu(Linux) and then runn XP and Vista from VMWare.

Later....

Ncix.com ran out of B3's and only ship G0 I heard.
Gigabyte P35C-DS3R doesn't overclock well? That's a first   They overlclock great. I'd get it over asus, save some money and get MSI 8800 GTX instead for $480.

Good luck.

EDIT: Forgot to add, if you are buying Z5300, X-fi would REALLY benefit you over onboard sound, Xtremegamer is fine.

For Dual Booting i'd do this: Install XP on one partition about 10 to 15GB big. Once XP is all good and running Install Vista on a partition about 25 to 30GB big (note: Vista requires 15GB of space off the bat to install so the extra 10 to 15GB of the partition is for breathing room for the OS). MAKE CERTAIN when you install Vista DO NOT make it upgrade but install on a new partition cause upgrading will of course override XP and that's not what your looking to do. So i'd say on your 500GB WD drive your set up should look similar to this:
C: drive - 15GB for XP
V: Drive - 30GB for Vista
P: Drive - 455GB remaining space for files/programs (of course you may have about 10GB less for formating purposes).

You'll Dual boot your machine and swith OS's as you please and have both use the P: drive to access programs. This is similar to my set up and I've ran into no issues. On one person's machine i set up they had a huge drive and wanted 4 partitions so I altered what i did above to this:

C: drive - 15GB for XP
V: Drive - 30GB for Vista
P: Drive - 220GB used for programs ran under XP
G: Drive - 220GB used for programs ran under Vista.

This set up basically allowed Vista and XP to run independantly and a lil more cleaner i guess for organization purposes. This is not really required but the person i built it for just was a slicker for ogranization and didnt want one drive to host programs used for XP and Vista (cause some programs didnt work in Vista). Hope this helps.

first of all i gotta say that gigabyte boards oc great ( from what i have seen) . but i also have to say i helped my friend hit 3.2 ghz on air with e6400 on the p5b duluxe wifi mobo so asus good too ( ddr800 6400 which turned into 5300 lol. corsair ram of course ).

second, don't even touch that q6600 quad core. get an dual core and get a quad core in the next year or 2.

great case.
i suppose you can keep that 550w psu. antec makes great psus.

switch that wD with a 500gb segate

switch the 640mb gpu for 320mb. you will upgrade in the next year so there isn't a point of getting 640mb when their will be something new next year.

stick with onboard audio. if you don't like onboard audio buy a sound card only after you tested the o.B audio.

I've just ordered a new computer (that is, I picked the parts and they'll fetch them and and build). It looks very much like the one the OP described. Mine will have an X-Fi ExtremeMusic. Now, what kind of speakers should I get? I could go as far as US$300. For example, is Z-5500 any good? Is it better than Z-5300, enough to be worth the difference? Is Altec Lansing still a good company? (I have 7-year old Altec Lansing ADA305 speakers and they're still great, but I want to try 5.1). Klipsch?

OP: I selected P35C-DS3R rather than Asus because Asus has some issues with quality and customer support. Mind you, most of the horror stories I heard were about the Striker Extreme, not about their P35 mobos. I totally agree with the comment about the GTX too (you may need a more powerful PSU but it's worth it).

The P35C-DS3R does overclock well. I read a review about it today and they had overclocked it pretty well on air cooling. Sorry I forgot where, I just typed "GA-P35C-DS3R review" in Google and found it.

Recently I build a pc with these specs:

Q6600 G0 stepping (no overclock yet)
Stacker 832 (7 120mm fans)
P35C-DS3R
2 gigs of Patriot Mem at 800mhz 4-4-4-12
320 WD AAKS
8800GTS 320mb 580mhz core
Asus DVD burner
Coolermaster GeminII cpu cooler with 2 120mm fans
700Watt OCZ power supply
=~$1450

Just a quick reminder to those looking to get boards that have DDR3 memory. You HAVE to get DDR3 memory sticks on it as well because it will NOT take DDR2 sticks. The module slots for the memory physically cannot take a DDR2 stick because of the notch changes in the design (this was done on purpose so no one could put DDR2 sticks in a DDR3 slot). I've just been seeing alot of people post machine specs for potential builds and they choose DDR3 boards but choose DDR2 memory sticks. Me personally, i'm going to wait on going DDR3 for another year or two now that DDR2 1066 and 1333 modules are coming out. Just don't make this critical mistake guys.

The P35C-DS3R has 4 DDR2 and 2 DDR3 slots, so that won't be a problem with that particular motherboard.

I got a (somewhat) related question: does anyone know if I can reuse my old IDE hard disk and DVD-RW drive in my new build, i.e. with the GA-P35C-DS3R? Thanks!