Unfortunately, this old motherboard is an absolute pile of $*&# - you cannot specify what mode the disk runs on, and from what I can google it's suggesting that AHCI isn't supported anyhow, so it's running it in IDE mode. Hopefully we're getting there now. Any thoughts on the "Windows cannot be installed to this disk" message would be much appreciated though.
Really appreciate ALL of the thoughts and suggestions so far.
You might be able to install Windows to that drive anyway. The other day I was installing Windows 8 to a VHD and it gave that error, but I was able to ignore it and install Windows on it.