To add to this here is what I've done:

- Disabled UAC

- Added everyone to "Log on as a Service"

- Ran install from both mounted ISO and from an extracted ISO located on the server.

- Uninstalled Antivirus (Forefront Endpoint Protection)

My current setup is this..

Windows 2008R2 VM, latest patches.

Server currently has these roles:

- SSO 5.1

- Inventory service 5.1

- vCenter 5.1

- Update manager 5.1