Well, the driver supports both XP and Vista, there is not a separate download for either. And the driver do work in both OSs, as I have a testmachine with Vista running using this driver. But the problem is, as the OP describes, that the machine sortof hangs while still in XP, I guess it's when the ghost service process tries to add the ghost-boot in the mbr things go wrong. And said IaStor0 timeout msg in event viewer.
Anyway, I had to bite the bullet and change AHCI to IDE. I'm not happy about it, it took extra time I really didn't have, and it doesn't solve the problem. Seems like AHCI-mode still is a bit of rocketscience. It was a similar experience when we bought Dell Optiplex 755, we had to change to IDE because there was problems getting it to work with AHCI.
One can always hope GSS 3 will work better .. but at that point we're probably running Vista, so that might be a moot point. Thanks for the tips anyway.