fyiOver on the System Center Operations Manager product team blog, Rob Kuehfus (Setup and Deployment Program Manager) posted a great chart containing the details on installing a Windows Agent or upgrading a Agent from the command line.  Check it out straight from the source here:

http://blogs.technet.com/momteam/archive/2009/07/08/windows-agent-install-msi-use-cases-and-commands.aspx

J.C. Hornbeck | Manageability Knowledge Engineer