Hi,
first of all hello to all of you as this is my first post here even if I have been reading the forums for some time.
And a great thanks for activating my account.
Well, coming to the point, I took some time during my holidays to build my new system.

My hardware is:
cpu: q9450
mobo: p5q3 deluxe wifi @n rev 1.02G
gpu: hd4870
psu: enermax modu 82+
Case: silverstone cw02
cpu cooler: thermalright hr01 plus
fan: noctua s12
ram: corsair TW3x4g1333c9dhx
hdu: seagate 500gb (sata)

I'm experiencing great problems (which is an euphemism, as the system doesn't work).

I have had several attempts in installing Vista 32 bit (system freezed, BSODs, etc) and after like 20 of them it has finally installed.
I had to use just one memory module (2 Gb), inserted in dimm B1. Bios flashed via Ez utility to, at that time, latest rev. 1103.
The system has a fresh Vista Premium 32 bit licensed installation. The only thing I have then installed is Catalyst 8.7.

However the system is very very unstable: it crashes after a random period of time (it could be from 1 minute after having log in to some hours of usage - maximum was 4 hours). I get a BSOD (IRQL_NOT_LESS_OR_EQUAL) or the screen goes black or with green stripes. In all these circumstances I can only hard reboot.
I have flashed the BIOS to the latest rev (1201): still no luck.

Already tried several settings, as posted and read on many boards. Manually set RAM parameters (1333Mhz, 1.70v, 9-9-9-24,2T etc), cpu voltage (1.20v), nb voltage (1.20v)...
Booting in safe mode the system seems running fine, even if it did some BSODs even there (this is strange...). Cannot intall SP1 cause it takes long time and a crash arrives first.
Tested RAM modules (one by one) with memtest as suggested on Corsair forum: no errors at all after like 8 passes each.
I'm going crazy cause I'm not able to find what is the problem: is it the graphic card? is there a compatibility problem between Mobo and memory(it was in the QVL!), as it seems reading over the Internet and this thread? What else?

UPDATE: Further tests done
Tried to recable and change slots (where feasible) to all the stuff: no changes.
Tried to install Vista with the integrated SP1 on a new SataII hd: same problems. Installation freezed many times before success, and even after that when the system was up I got BSODs, black screens, etc. Same panic.
Tried XP Pro SP2 on an IDE hd: as above. Conclusion: at least is not an hd/OS issue.
Installed my RAM, PSU and GPU on a friend rig (X38 based), all worked fine.
So a possible conclusion is that it's the motherboard to have problems (ot at least the new intel P45 chipset).

I'll never buy again such a brand new stuff. I'm very disappointed, I've always been satisfied with Asus Mobos, but I think this time they have started to sell a product which is still not ready for the market. I see many posts about people experiencing huge stability problems with this mobo.
I'm thinking to RMA the product, cause it's 2 weeks I'm trying to let it work without any success....
What do you guys suggest me to do?
The last thing I can try is bring the system to a pc assistance center where they have spare parts and can perform more accurate tests.

Yesterday I finally got a response from ASUS R&D technical experts, here's what they wrote me:

Dear customer,
we have checked your issue into our labs, and it seems there is no problem:
we don't have same RAMs so I used Corsair DDRIII 1333-1G * 4 & Samsung DDRIII 1333-2G * 4 to test.

Test 1:
Q9450 (C0) & Corsair 1333-1G * 4 Memory OS installation pass,and Aging 3DMark06 3hours PASS,

Test 2:
Q9450(C1) & Samsung 1333-2G * 2 Memory Aging Sleeper 12 hours & 3DMark06 4hours PASS,

Configurations:
MB: P5Q3 Deluxe/WiFi-AP
BIOS: 1103
VGA: ASUS-EAH4870/HTDI/512M/A
VGA Driver: Catalyst 8.7(V8.512.0.0)
CPU: Q9450 (Q7UP C0) & (QEGB C1) 2.66G/1333
Memory: Corsair CM3X1024-1333C9DHX 1GB *4 & Samsung M378B5673DZ1-CH9
HDD: Seagate ST3320620AS
OS: Vista 32 bit
Verify if changing the VGA the issue still goes on.

Thanks in advance for any help, it will be more than appreciated and sorry for my poor english and this long post.