For some reason XP x64 is ruining my overclock thats PERFECTLY stable on XP x86. Please read this thread, i will not re type the whole thread here as its huge (and still not fixed).
 
http://www.overclock.net/windows/3 [...] lease.html
 
Please read over the thread and place your replies here, be sure to fully read the thread before asking "did you do this, did you do that?". Thanks in advance.

That's bizare. I run XP 64 and have my Q6600 OC'd. I haven't used Orthos, but Prime 95 works perfectly fine. Even when trying to OC I never got a BSOD. Only times I've ever had  BSOD with XP in the past was related to memory problems (ie bad chips).
 
There's got to be something that is running or working differently from x86 to x64 that's causing the problem though.
 
I will say though, I tried running the Intel TAT program yesterday, and EVERY time I try to start TAT my computer immediately reboots without displaying any error or BSOD. LOL So maybe TAT doesn't work with x64? Or with Quads even...
 
*EDIT*
 
Just got done reading all 6 pages of your original post @ Overclock.net. I'm still wondering if it isn't a memory related problem. Since x86 won't use all 4GBs of your RAM, the x64 might be finding a hardware issue in one of the memory chips.
 
Maybe try taking 2GB of memory out and trying it then. I'm just curious as to whether the OS simply isn't using the portion of one of your dimms that has a flaw.
 
*shrugs* Aside from that, I don't think I'm technical enough to help ya.