Buddhism is a religion that is definitely growing. It is now the 4th most practiced religion in America and has 350-500 million adherents worldwide. Because of this, one must be prepared to be able to respond to a Buddhist's objections to the Christian message and respond accordingly. To do this, it is very good to have a grasp of the teachings of Buddhism.
The following resource from AlwaysBeReady.com can either be read or listened to, and contains a great overview of the history of Buddhism and its teachings. Also it contrasts the Buddhist religion to Christianity and gives tips on how to witness to people of that faith.