The definitive Problem

Hi guys,
I'm afraid you're my last hope. I've bought some components recently and assambled myself a nice rig, problem is, when trying to install an OS I cannot. I'll describe what I have and what I've tried so far, if you can give it a thought and give me your two cents, I'm open to ALL suggestions.

The bits:
Thermaltake Spedo Advance with added fans.
intel Core i5-750 // Noctua NHU12P (untouched running at stock speed)
Asus P7P55D-E Deluxe
2x2gb Geil 1333 Ram CL7 (untouched)
Sapphire HD5870
WD Sata Drive 500Gb
1000W Cooler Master PSU

Peripherals:
Samsung T240
Razer Mamba
Razer Arctosa

Basically Win7&Vista both x64 & x86 give a Random BSOD (code error is different every time but Bad Pool Header seems SLIGHTLY higher in occurrence) during installation.
XP64 completes installation 90% of the times but suffers from a general senso of lag and eventually after a while starts crashing and bsod.

OS I've tried:
Vista x86
Win7 X86
Win7 X64
XP X64

Solutions I've tried in searching for the reason to all this:

Updated Bios to latest release
Unlugged every peripheral but a Ps2 keyboard
Used a different DVD drive and a Different HDD
Used both the drive and the HDD on IDE (I assumed it could have been the sata controller)
Removed a DIMM trying to use only one
Tried almost every combination of sata ports for the drive and the hdd

Cooling is not an issue the bios reads 37C on the CPU and 33C on the mobo.

Help me guys please I'm starting to lose it...

A small update, running a Deep scan memtest...at 3 complete cycles no problems so far...will complete 5 cycles though...

Nxt up I'll try to hook an old GPU.