I forgot this!

This approach will go part of the way to what you are after:
  • Create your box or a new Layer in the place you want it to stop at.
  • On the MouseOff layer add a clickable shape/button.
    • For this, set its Web Properties > Link > Pop-up layer to the new Layer.
  • Click its Settings... button.
    • Change the transition to Slide in from left.
    • Change the Speed to 5.
    • Untick Close pop-up automatically.
  • Click the OK button twice.
  • Preview
Acorn