I have now solved this problem... After booting a Debian live DVD I compared the xorg.log's and found an anomaly... The machine was still using the old kernel, despite having done a clean install.. and believing it had correctly installed the new version of grub (It hadn't). After running grub-install /dev/sda (and update-grub to be on the safe side) it booted the newer version of grub.. showing the correct kernel version.