Ben Armstrong to the rescue.  He writes:

The Virtual Server Administrator's guide outlines how to perform a basic unattended installation of Virtual Server.  However it does not tell you how to do a customized unattended install (where you only install some of the components).  You can do this with the following command (all one line):

msiexec /I "Virtual Server 2005.msi" /L*v %TEMP\VS2005Install.log ADDLOCAL=VirtualServer,VMRCClient,DevAndDoc,VSWebApp PIDKEY=#YOUR_PID_WITHOUT_DASHES# /qb-

Where you remove the components from 'ADDLOCAL' that you do not want installed.  So if you just wanted the VMRC client you would run:

msiexec /I "Virtual Server 2005.msi" /L*v %TEMP\VS2005Install.log ADDLOCAL=VMRCClient PIDKEY=#YOUR_PID_WITHOUT_DASHES# /qb-

Note: To get the .msi file with Virtual Server 2005 R2 you will need to run Setup.exe /c /t [drive letter]:\[path to the .msi file].

Please visit Ben Armstrong's Web site for more information like this, and please thank him and comment on this tip, by going here.