Planiverse: Computer Contact with a Two-Dimensional World by
A.K. Dewdney.
Planiverse is a book that features a group of college students and their teacher. The students created an artificial intelligence program that simulates creatures in their own world.. the "Planiverse". As you probably guessed, the creatures aren't very intelligent. They perform simple functions like "HUNT" and "F.E.C. IN FOCUS", which tells the user which creature they are looking at.
One day, one of the students focused on an F.E.C.. When focused, the F.E.C. replied with the word YNDRD. This YNDRD seemed to be growing in intelligence.
As the group continues conversation with YNDRD, they come to realize that they have tapped in to an actual parallel universe. The book is based around the group's thirst for knowledge and YNDRD's spiritual maturity.
The author creates a two-dimensional world near perfectly. With it's own physics, culture, and climate, this book will keep most sci-fi buffs entertained for hours.
If you would like to order this book, try http://206.67.72.201/catalog/np/sep99np/0-387-98916-1.html