|There are a few major problems with doing this.....|
Firstly you could probably build a list of the most common anti-virus software an try to detect them via the default install directory. The problem with this method is that unknown anti-virus software will go undetected, the anti -virus could be installed to a custom directory or worse still when a new version is installed/upgraded it could be installed to a new directory.
I haven't looked into much but it may be possible to let the security center in xp sp2 and above do the work, but it would need to be programed in a language that can access the windows api. It might be possible to make a console utility in c/c++ that could be run from a batch file to achieve the desired result.
Like I said though I haven't looked into it much but my guess would be to look at WscGetSecurityProviderHealth
I just realized that function is vista only - woops....