mrmovie,
When working with WMI, to find out what what methods of a class are read only I use a little known but very powerful tool that is already in Win 2000/XP. Here is how to pull it up.
Start---->Run----> type "wbemtest"
It will pull up a small interface click on Connect. It will ask what namespace you want to connect to, put in root\cimv2, click Login. It will bring you back to the main pop-up but all the buttons are available now. Click on Enum Classes, it will bring up a pop up, select the recursive radio button and click OK. It will then bring up the top level classes in the namespace that you choose. Now scroll down and select the Win32_NetworkAdapterConfiguration and doubleclick. It will pull up a very interesting dialog box. In this box at the bottom, it will list all of the methods available in that class, double click on one and it will tell you more indepth info about that particular method. Usually based on this info I can tell whether it is read only or not as well as many other useful items with WMI scripting. The only thing that I don't like is that you cant maximize it to avoid all the scroll bars, but Oh well.
HTH
Z