For all of you that are new to BDD 2007 (and some of those that aren't) I would highly recommend getting your hands on the "Quick Start for BDD 2007" white paper. As it says it will help you quickly get started with BDD without the need for wading through the BDD documentation. This can be obtained from the BDD download site here. The document is not included within the BDD MSI file but can be downloaded from the same web page as the BDD 2007 MSI.
There is also a second white paper available in the same location that is worth a read called "Windows Vista Deployment Tools Overview". This provides an overview of the numerous tools that BDD leverages to perform deployments.
Note: I would strongly recommend that you take the time to review the BDD documentation, it is full of great information and resources. You will find this documentation located in the BDD folder after installation(.\BDD 2007\Documentation).