The exact place it was used in the movie is at the snail love making section.
If u want to listen to it
U can check it out at:
Amazon.com: Microcosmos: Music: Bruno Coulais,Kristin Scott Thomas,Marie Pérennou,Claude Nuridsany (http://www.amazon.com/Microcosmos-Bruno-Coulais/dp/B00005QX0F/ref=sr_1_1?ie=UTF8&s=music&qid=1199459415&sr=1-1)
The song is number 4.

I found it , so u can stop looking lol..
It's called Amour d'escargots, by composer Bruno Coulais .