MY PREVIOUS POST IS TOTAL (INSERT YOUR OWN CHOICE OF WORD)!!!
Using a status check to turn horizontal/vertical scrolling on and off just using Alex's viewport function does work ...so does Simon's backdrop code (providing you initially define portx and y) but it's more like a nightmare!!!
Start the game with the status set to 'no scrolling' and not setting the viewportmode to 1 just makes the background tile center around Dizzy as he walks ...the rooms still act like the viewportmode is turned off.
Then, when it all seems to work fine ..switching the vertical scrolling on for Dizzy to go down a hill makes him vanish when he leaves the 'room' and the bottom half of the room he's just left vanishes too so that it just looks like someones sliced off the top of the hill (cos the background is still following Dizzy around).
Oh well, looks like I should leave proper tech stuff to the adults.
PS - this is my face when I looked at Colin's scrolling code in 'A Pirate's Life'
Need help with using DizzyAGE then look here