This can be done with VBA. If you want to use multiple choice review
questions to test their knowledge, check out my free sample (bottom one) at:
http://www.pttinc.com/cbt_development.html
I also have a sample download on calculating within PowerPoint at:\ the link
below. It will show you the code on how to manipulate control toolbox
objects to get different results.
http://www.pttinc.com/ppt_faq8.html
Basically you would have to create your smiley face, name the object so you
can set its visible property to TRUE or FALSE. Create your textbox control
for them to type in, put another button on the slide to "Check Answer". Set
a macro to run that has some sort of "If, Then, Else" or "Select Case" to
determine if what they typed matched your code, and if it did, show the
smiley face or do something else. You're only limited by your imagination
(and knowledge of VBA)! HA!
Holler back if you have questions as you pursue this.