It is best to check Microsoft server software and supported virtualization environments:- http://support.microsoft.com/kb/957006/ before you decide to virtualize your environment. Only those product listed in that site is supported by Microsoft.
Besides that, vendor who listed in Server Virtualization Validation Program (SVVP) :- http://www.windowsservercatalog.com/svvp.aspx?svvppage=svvp.htm will get support from Microsoft.
If any problem arise and it is not listed in the above site, you will need to test and simulate in physical environment before contact Microsoft.
So check it out before deciding on going for virtualization.