I posted an updated script at http://community.kaseya.com/resources/m/knowexch/57536.aspx
Go to page 4 to get the updated script that works on XP, 7 and 8, using the Windows Security Center
I look forward to testing this.
I'm currently updating some scripts that will check for various versions of AV. I'm using MSPAssist scripts as the base but rewriting everything to make it either more efficient while running or to address any reporting issues that I find.
I'm about halfway done and I hope this script will work to replace the WMI script that is frankly hit or miss. Not a fault of the script but more of an issue with the workstation not wanting to give up that info. :)