Mr.Pandah said:
Memtest is a great program to test if you have bad sectors in your memory, but I generally go with the simpler appraoch of taking out all the sticks and trying them one at a time. Secondly, Vista sucks (matter of opinion). I had so many problems when I tried to use Vista from Windows XP Pro that I reverted back the same day.
When was the last time you reformatted? Sometimes Windows can be a pain the arse. I keep my Windows installed on a seperate partition from the rest of my files so that I can reformat every 6 months to a year to keep a clean install going.
Are you getting any crashes while using the computer? Are the temps on your SLI'd 8800's at a decent clip? You'd be surprised what can cause issues. I have two 8800GT's SLI'd together and they put out an insane amount of heat. I had to up their fan speeds to 100% all the time and install 2 120mm case fans right above them to keep them at nominal levels.
Do you have a firewall going at all times? Have you recently done a virus scan, and what anti-virus program do you use? The Vundo virus (and it's close relatives) can mess hardily with your computer and do all sorts of fun things. It's actually fairly common to get, especailly if you pirate games at all (not implying you do, but there's a chance) and can be a pain in the ass to get rid of.
You said you've tried both the DVD's as well as downloaded installers. Is this only with WoW or have you tried other games as well? When you got the new harddrive did you just slap it in as a secondary drive and try installing the game there, or did you take out your old one, put the new one in, install a fresh copy of windows and then try installing?
What size power supply do you have in it? What's the total Amps it puts out? If I remember correctly, having dual 8800GT's SLI'd takes upwards of 50+ Amps on the 12V rails and not having that can make a system incredibly unstable.
In short, there's so many factors, with out messing with it myself it's hard to diagnose. (I have 3 computers at home I've built from scratch and have had to troubleshoot them all at times, hell my wife's motherboard came DOA, took me 2 days to make sure it was the mobo and not another component)
BTW, what's your SSN, Driver's License, and bank account numbers? Hrm, no? Damn, thought I could sneak those questions in there too. =P joke >_<