Hi,
If you are using ESXi and booting from a non local disk, you must first pre-load the additional drivers as per ESXi to allow the Windows 2008 host to see the disk to which it is installing.
Also a point to note, if you are using thin provisioning on the ESX you must configure the initial size of the thin device to the minimum hard drive spec of the release of Windows server that you are installing.
Hope this helps :-)
M