If you install Microsoft Virtual Server on a “server” machine and after
starting a virtual host on the machine you lose all network connectivity to
the “host” machine you should read the following:

http://support.microsoft.com/kb/888750

It indicates that VS2005R2 has an issue with TCP segmentation offloading or
other “offloading” to the NIC … so you have to disable those features of
your network card to maintain connections with the “host” machine.