Here is how to detect the Operating System(OS) the client is using. It will work on both IE and NN. This larger script stores a two digit abbreviation for the OS in the variable "clientos" for you to reference. The valid two digit operating systems that will be reported when variable "clientos" is referenced are:
For Windows: "31", "95", "98", "NT", "2K"(2000) or "XP" For Macintosh: "MA" For OS/2: "OS" For Unix and Others: "UN"
Alternately you could execute some code instead of setting "clientos" variable. Here is a simple example where you don't need to store the OS for later. It redirects the browser to one page if the OS is Windows, a different page for other systems.
Anyway, I hope this helps those that want it.