A week into my new build and I'm ready to throw in the towel. All items purchased from NewEgg.
ASUS P5N-E SLI LGA 775 NVIDIA nForce 650i SLI ATX Intel Motherboard - Retail
Intel Core 2 Quad Q6600 Kentsfield 2.4GHz LGA 775 Quad-Core Processor Model BX80562Q6600 - Retail
Crucial Ballistix 2GB (2 x 1GB) 240-Pin DDR2 SDRAM DDR2 800 (PC2 6400) Dual Channel Kit Desktop Memory Model BL2KIT12864AA804 - Retail
Crucial Ballistix 1GB (2 x 512MB) 240-Pin DDR2 SDRAM DDR2 800 (PC2 6400) Dual Channel Kit Desktop Memory Model BL2KIT6464AA804 - Retail
EVGA 512-P2-N773-AR GeForce 8600GTS 512MB
Rosewill RP600V2-S-SL 600W SLI Ready-ATX12V V2.01 Power Supply - Retail
Seagate 500GB SATA for boot/OS drive and two Seagate 500GB IDE drives for data storage
SAMSUNG 20X DVD±R DVD Burner Black SATA Model SH-S203B - OEM
COOLER MASTER Mystique RC-632S-KKN1-GP Black Aluminum/ SECC ATX Mid Tower Computer Case - Retail (two 120MM fans)
Two 90MM side fans blowing on the CPU/NB/GPU (praying it'd help)
WinXP Pro SP2 is on it currently
As best I can tell the problem is fully between the board and the RAM. I've never had so many issues building a system before and I'm leaning towards swapping the board with something else, though I have no idea what. But probably not another ASUS product though I've always used their boards in the past. Anyway...
I'm currently running BIOS 803 on default settings with ony the boot settings adjusted so it'll boot from my CD first, then SATA, then IDE drives as I've tried everything else I can think of and that I've read from manually setting voltages, memory timings, disabling various BIOS features. The only thing I haven't tried at the time I write this is reducing the RAM speed from 800Mhz to 667Mhz which I'll try but that just seems downright stupid that I'd have to do that at all.
I've tried a single stick of RAM in various slots. All of the RAM installed as it should be for 3GB dual channel setup. Memtest usually passes one stick at a time. But as soon as I get into dual channel setups it claims errors. I'm having random BSOD, GPFs, you name it.
The problems are at their worst when I have all 4 sticks of RAM in there. The most crazy behaviour is all is that the CPU gets blazing hot (idles in the mid-50C and Prime95 can send it well past 70C in mere seconds) with all 4 sticks of RAM installed in dual channel mode using 800Mhz 5-5-5-15-T2 settings at 2.2V. The RAM is supposed to run at 800Mzh 4-4-4-4-12-T2 @ 2.2V for crying out loud. Running a single 1GB stick with default BIOS settings and Prime95 pegs the cores at between 60-66C and idles in the 40's. NB is currently at 39C but idles in the 50's with 4 sticks in there. I'm just finding it INSANE that this board goes so bonkers with 4 sticks of RAM in it. If I have more than one stick in there and don't manually set the timings the board usually won't even POST it just hangs with a long beep.
Anyway, before I throw in the towel I'm hoping for some suggestions other besides both under-timing at 5-5-5-5-15-T2 AND under-clocking the RAM at 667MHz. I'm just in disbelief I'd have to more or less cripple the RAM to pacify the board.
Note I'm not even shooting for OC here at this point. I just want the damn thing to run stock and not crash multiple times a day.

I've spend way WAY too much time pouring over data on forums trying to crack the case on this machine.
P.S. I've tried for days to register on the actual ASUS forums and their board keeps reporting "server too busy" whenever I try to register. Another nail in the coffin for my ASUS love. Hard to believe they could kill it so badly with one product.