Can't be done in DVDA without assistance from another program. Here's what I think you'd have to do:

You would have four menus with these buttons (the names are just an example -- call them what you want):

Movie One
Movie Two
Movie Three
Movie Four

For each copy of the menu, one button would lead to the appropriate movie while the others would lead to a different copy of the menu (and each of those would have a similar but appropriate set up). And for each menu, you would add the backgroundaudio that you want.

Now, at this point, you have to actually hightlight and select a button in order to move to a different menu (which is how you get the background audio you want). If you want the menu switch to take place automatically upon selecting a button, you need auto-actions, which DVDA does not provide. After you've designed and prepared your DVD files, you can use MenuEdit to edit the menu's VOB file (it's probably the smallest and lowest numbered file) and change the buttons to be auto-activated.)

Keep in mind, though, that switching between menus takes a second or two on most DVD players, so your viewer is going to have to wait for that pause everytime they move from one item to another. I personally think this would be a bit annoying, especially if they're just trying to move between non-adjacent buttons. Your perogative, though. :)

Unfortunately, this is really the only way (as far as I know). There's no way to allow for the viewer to just "change" audio for the current menu. The audio is part of the menu, so you have to make them actually switch menus if you want a new backgound audio or want to play a sound. BTW, this is not a limitation of DVDA, it's just the way DVDs are. (Except for the auto-action part...that is a limitation of DVDA. Probably should've been added when they added end actions, but oh well.)

Rob