Is there are reason why you're not using a software GPO to handle the Installed/NotInstalled issue?
It's a lot slicker than running a stub of code to see if the application exists. Besides, that way you don't even have to download the stub of code to see if you need to do the install. Pro: When you have to revise the software, you can use a GPO to make the update optional or mandatory, including removal of the existing version. Really neat-o.
The downside would be that you have to turn the installation files into an MSI.
Another downside --- the Win98 workstations would NOT get the software.
--Woodie