Force users to view all rollovers before moving to next screen

There are a couple of options.  Rollover captions and rollover image objects are unable to trigger advanced actions on rollover, but you CAN do this with rollover slidelets.  So you could set up variables and advanced actions to track whether or not the user has viewed all rollovers at least once before showing a button that allows them to navigate to the next slide.  If you want to avoid rollover slidelets (due to all the issues they bring) you can use Event Handler widgets from Infosemantics.  Attach the widgets to the rollover caption or rollover images and this allows you to trigger advanced actions but with much more flexibility than with slidelets.

One caveat.  None of these solutions work in HTML5.