Several Distro Specific Links Here:

http://blogs.technet.com/seanearp/archive/tags/Linux/default.aspx

Red Hat EL Here:

http://blogs.msdn.com/virtual_pc_guy/archive/2006/08/08/692395.aspx

Linux System Clock Issue in VPC:

http://support.microsoft.com/Default.aspx?kbid=918461