Ok here's my quick & dirty solution:
http://www.theroboz.com/kinoko.zip - everything is in the room script
One problem I found using the room bg as the bottom layer is that then the object you use as the floor (topmost parallax layer) will actually move faster then your character intended speed so, when the scrolling stops, your char looks as if he's suddenly slowing down...
Instead I use the room bg as the topmost layer and fake the parallax using two objects and the bg walkbehind... depending on the layout and dimensions of your room, this could be ok also for you.
Anyway check the sample (tested with AGS 2.71 rc3) then let me know.
http://www.theroboz.com/kinoko.zip - everything is in the room script
One problem I found using the room bg as the bottom layer is that then the object you use as the floor (topmost parallax layer) will actually move faster then your character intended speed so, when the scrolling stops, your char looks as if he's suddenly slowing down...
Instead I use the room bg as the topmost layer and fake the parallax using two objects and the bg walkbehind... depending on the layout and dimensions of your room, this could be ok also for you.
Anyway check the sample (tested with AGS 2.71 rc3) then let me know.