Well, this is a tough one! I remember reading some story about two characters Frog and Toad when I was in Kindergarten. And the Librarian at my Elementary school simply oozed with a love of books that I drank of deeply, even at that young age.
However, there are other steps which built up this love even more. When I was in 4th grade, one of our local tv stations advertised for kids to write in for a free set of Apple/Scholastic books, which I did all by myself. And the joy when they actually arrived in the mail was very much involved with the joy of books in general. During those days I read a lot of Encyclopedia Brown and The Three Investigators series', and the difficult vocabulary of the latter inspired me to increase my own.
However, I also used to watch a lot of Reading Rainbow, and loved the parts where the different children would give little synopses of varied books, and that just enflamed my booklust even further. So, there really isn't any one episode where my booklust began, but rather a whole youth of episodes that created the Bibliophile I am today.