It can be done with use of custom css and js (you need to set div position to absoule, and then check while scrolling how much have you scrolled and run animation when needed).
It is already done in "Simplicity" template:
http://demo.gavick.com/joomla25/simplicity/when you scroll - laptop image slides in.
You can use css3 transitions to animate slide in automatically basing on element top/right/left beginning and ending position (which means adding a class with js when window is scrolled enough should do the trick)