“The earlier Kabbalah tried to bring man into heaven. The main idea of Chassidus was to bring heaven into man.”
Chassidic thought is predicated on Kabbalah, Jewish mysticism, but Chassidic works differ greatly from Kabbalistic tracts. Chassidus emphasizes practical application while Kabbalah describes Heavenly domains.
613.org (Audio Torah site) presents the first half of a new book online:
Flames of Faith: An Introduction to Chassidic Thought (Adobe Reader required)
While I've only read the introduction, it looks like a very nice introductory read to the topic.
BS"D - בסיעתא דשמיא