On the campaign selection screen, there should be a scroll next to the campaign names, and it should now allow you to scroll down the list to the XL campaigns. Unless, of course, you installed the mod wrong - so, make sure that you install directly into the base MTW folder. On my computer, it's F:\Games - Medieval Gold Edition that I installed into. No subfolders, just the main folder where you access the .exe from, and can see all the other folders and some of the .txt files.