Even though this is a Windows related question on a physical host, I moved the discussion from VMware Workstation to Virtual Machine & Guest OS
On a Windows system which is not part of a domain you may use e.g. the win32tm command line tool to configure a time server. I'd recommend you synchronize the Windows system with the same time server you used set in the NTP settings of the vSphere hosts.
for the w32tm syntax, see http://technet.microsoft.com/en-us/library/bb491016.aspx
André
