OK, I finally got it to work! Many thanks to all of you, especially HatchetMan for your links. Although I do have a problem...
I found the first guide listed too difficult as I was unfamiliar with PGC Edit.
The second guide explained eveything but was more complex and also designed for main movie, and adapting it for menus had quite a few diffences, not all of which were fully explained.
BUT... guide no.2 helped me get familar with a few things so I was able to have another crack at guide 1, which has worked!!
The thing is, it only works when the DVD is inserted. If it's been stopped then played again, it goes back to its old habits. Is there a way to make it so it happens on every time the disc's played as opposed to put in???