Need help diagnosing PC problem

After seeing my Shammies in action, a friend has upgraded his PC to start 5-boxing.

However, he's having FPS issues just running 1 WoW :(

His PC spec is:

• Intel Core 2 Quad Q6600 Energy Efficient 95W edition Socket 775 (2.40GHz) G0 Stepping L2 8MB Cache - running at stock settings
• ABIT IP35 Pro iP35 Socket 775 8 channel audio ATX Motherboard
• 8GB RAM (4 x 2GB OCZ DDR2 1066MHz/PC2-8500 Reaper Memory HPC Edition Dual Channel)
• 512MB Inno3D GeForce 8800GT
• Coolermaster Silent Pro 700W Modular PSU
• Samsung HD502IJ SpinPoint F1 500GB Hard Drive SATAII 7200rpm 16MB Cache
• Creative Soundblaster X-Fi
• Dell 24" TFT @ 1920x1200
• VIsta 64

It's a fresh install of Vista64 and the latest nVidia drivers for Vista 64 (release 175.19 from 23 June) running a single WoW in windowed mode 1920x1200.

I have a worse spec PC (E6600 / 4GB RAM / XP32 / 640mb 8800GTS) and he was seeing huge stuttering during a dungeon run with me yesterday when, for example, 4 fire nova totems went off simultaneously).

We'd compare FPS looking at the same part of the dungeon and I'd be wavering around the 57-62fps and he'd be down at 29-32fps!

Things already tried:

• completely disable all addons - made no difference
• check the config file for rogue maxfps settings - none found
• enabled hardware sound in WoW - probably added 2-3 fps

He's very disillusioned that, after building such a high spec PC, it's having such problems running a single WoW... he's not even going to activate 4 new accounts until it's sorted.

So... does anyone have any ideas what could be causing the problems?

Any help very gratefully received from a potential new 5-boxer.

Was this a fresh install of wow or was it copied across from another location? if it wasnt try deleting the WTF folder and give it another bash. sorry i cant be much more help as i have never used vista 64.

Should also try checking the driver for the graphics card.. And try deleting the "cache" folder..

try downgrading the driver to 175.16 as the .19 has some issues with framerates on certain machines

Do what everyone has said so far. If that doesn't help, make sure you have UP TO DATE DRIVERS on everything. If that doesn't do it still, reinstall WoW.

Thanks all.

I've sent him a link to the 175.16 drivers to try as a first step.
If that doesn't work, I've told him to reinstall WoW from scratch (as this was a migrated WoW from his previous PC incarnation).

Fingers crossed!