you should do something like:
the screen width is 600
the image width is say 850
diffrence=850-600
ratio# = diffrence# / 600.0
scroll_x# is the location of the slider
drawblock image, -(scroll_x# * ratio#), 0
the screen width is 600
the image width is say 850
diffrence=850-600
ratio# = diffrence# / 600.0
scroll_x# is the location of the slider
drawblock image, -(scroll_x# * ratio#), 0