Hey man,
Have you tried Bootvis (assuming you're using XP)?
No.11 in this list. My mate had a Asus
AV8 mobo that came with his Alienware machine. I know it's not the same model, it's just a similar problem.
His machine can take up to 5 minutes to boot - it seems to just sit on the animated Windows XP screen. He brought his PC round to mine for a repair of something completely different yet still motherboard related, and I borrowed his graphics card to do an SLI setup on my machine and stuck an old nVidia card in there for the time being. The boot time dropped to 30 seconds! I then tested it on an old ATI card, and again, 30 second boot. I then tried my graphics card, which is exactly the same model as his, which boots fine with my mobo, and it went back to a 5 minute boot again.
Where am I going with this?
It was just a freak incompatibility that I couldn't solve, even after flashing the mobo bios and trying different driver revisions. At that time I'd never heard of Bootvis, so I don't know what it would have shown.
Chuggers