There's no AHCI in the BIOS of the motherboard, but the PCI card came with an install routine that reckoned it fixed all that - for Vista. I ran that, then updated it with the latest version from the VIA website. Made no difference.
Folks I've spoken to played for a while with AHCI and got no further, so I didn't spend long on it.
I've put the card in its box and relegated it to the workshop now. The drive is USB until Verbatim answer my e-mail. Life's too short!