At the time, a way of installing the VSphere client was identified: "set the Compatibilty on it to Windows XP SP3 and set the priviledge level to run as administrator.". Only a partial fix as the console view did not work, but it was good enough for my needs at the time.
Since then, VMWare have releaseo a later version of the Server (ESXi5.1.x) which fixed the console issue for me. Downloading/Burning the ISO installer, and running the upgrade on the host was easy, and worked on the 3 hosts we have here.