I've finally figured out how to get a profile to load and turn on automatically with VAC using Il2Stab. This will probably be obvious to anyone with even the least amount of technical know-how but it took me over an hour to figure out .
Open Il2Stab 'Options'.
Click on the 'External Applications' tab.
Right-click on the space and select 'Add'.
Use the 'Browse' tab to find where the VAC program is located, then select it. This will load it into the 'Executable' window.
Then click onto the 'Arguments' window, type in the name of your profile (it will be an .xml file).
Add ',true' at the end (no spaces!).
Click on the 'Autorun' box, then click on the 'Ok' button.
When that's done it should load the VAC program and profile, and activate it.
I read the VAC help file that talked about 'Command Line Parameters' but it didnt make much sense to me