Is it possible to add a Windows machine as a host?

Hello every one,

I am using VMware VSphere 5.1. Below is my setup

WIN2K8-ENT  -  DC (Domain Controller), running on Windows 2008 r2 64 bit.

WIN2K8-STD -   Hosting the Vcentre server, running on Windows 2008 r2 64 bit and part of the domain.

VMware ESxi 5.1 - A host machine in my data center and part of the domain

WIN2K8- HOST - Aother machine i want to try to add as another host in my datacenter and part of the domain.

Below is my problem description.

Already i have added the ESX 5.1 as a host machine and now i am trying to add Windows machine as another, but i am getting the below error message.

"Call "Datacenter.QueryConnectionInfo" for object "DCENTER" on vCenter Server "WIN2K8-STD.contoso.local" failed."

And i am attaching the compleate screen shot also.

Here i have a question.

1) can't we add a Wndows machine as a Host in Datacenter.If yes, why?

2) Which types of OS we can use as a host machine?

Thanks,

Vishnu.