MOMNetCheck was a tool shipped with the MOM 2005 Resource Kit. It was a nice GUI tool but limited to pointing at one server at a time. I have been working on a MOM 2005 project where a multiple server tool would have been very handy.
Satya has released a command line version of a new tool for OpsMgr 2007 and it works from the command line and can do multiple servers. Hurrah!
It checks for the new prereqs like MSXML v6.
Read about it and download it at http://blogs.technet.com/momteam/archive/2007/11/20/remote-agent-prerequisite-checker-tool-for-opsmgr-2007.aspx