that should be fairly simple.  you just need to add an additional plugin to the autostart section.   it is called Task Create/Switch Events.  right click inside the autostart section and choose add plugin.

once this plugin is enabled, whenever you open a program, or switch back and forth between a window, you will see a trigger on the left side of the screen.  drag that trigger over to any macro on the right side of the screen, and whenever that trigger shows up, your macro will run.  just look for a trigger that says:

Task.Created.iTunes