Currently when people are on the (vbadvanced) homepage there's a link in the navbar to the forums (www.site.com/forum.php, named 'forums'). As soon as they're on the forum, that link is changed automatically to 'home' (directing people back to the mainpage www.site.com/index.php).
But now with the gallery, the link in the original navbar is 'home' and directing people to the home of the gallery (www.site.com/gallery/index.php). But the link on the new gallery navbar is also named 'home' and is directing people also to the mainpage of the gallery (www.site.com/gallery/index.php).
So how can I change the main navbar so that when you're in the gallery the link says 'forums' and direct people to www.site.com/forum.php?
I added a Gallery and Forums link in the forum Nav bar, like above your post.
This simply allows users to travel to whichever part of the site they want. My original alternative was a category with the url direct feature pointing to the gallery index.php. The category was simply labelled 'Gallery'.
Gallery Categories dont support this, so I then looked into editing the Forum Nav bar which is simple enough. Just go to your forum template in AdminCP and edit the header where your nav bar links are...
[Edit:] After reading through your question again, I dont think I completely answered your problem, but it may help.