My mom teaches preschool at home, so, unfortunately, she is no stranger to things like this. She has something similar to what Laura suggested. It's called "Desolvit", and gets things like gum, play dough -- you name it -- out of anything. It's safe to use on skin and hair, so I'm sure it would be fine on carpet.
Good luck, Mada!
Local Coordinator, Utah
DH, Scott, 26
Maggie Lylas, 6/9/03, 29 weeks, severe pre-e