NT Login Script

Is there a way to search a computer for an installed software package before allowing it to log on to the network?

I would like to be able to disallow a workstation from logging onto my network if it doesn’t have anti-virus software installed.I would need this to be a batch file that can be added to the log-in script so that it could be added or removed as necessary.

Please include the appropriate syntax, as I am not very .bat or login script friendly.