Finally installed Windows 7 on GA-G33M-S2H
By chance, I found a solution.
I had just burned a stored ISO on Win7 32-bit to try an install with, and accidentally put the DVD back in, which then autoplayed.
It offered me the chance to install Win7 from within XP. I try to avoid this normally – I prefer to boot straight into the install – but this time I let it run.
It accepted my pointing to an empty partition, installed, and rebooted… And started up within Win7 successfully! It completed the installation, and rebooted a couple of times more. It retained my original XP partition, and correctly handled the boot loader to choose between the two.
So – it seems it’s the same problems that mysteriously stopped me installing Ubuntu or WinXP when I first bought the motherboard. I didn’t work it out then, and I haven’t now, but if it works, that’s good for me!
Now to try 64-bit…