VMware Woorkstation not supported on Windows Server 2008
VMware Inc., for one, won't officially support it on VMware ESX Server or on VMware Server until the third quarter – for at least another three months, Support for Windows Server 2008 on VMware Workstation could come even later
http://searchservervirtualization.techtarget.com/news/article/0,289142,sid94_gci1302139,00.html