Office Business Applications are really taking off. These apps leverage the comprehensive platform provided by the Office System. There's a great publication available from the guys at the architecture team at Microsoft.
Office Business Applications: Building Composite Applications Using the Microsoft Platform
This is available online on MSDN, as a download that you can read offline or in hard copy. If you really want a hard copy, drop me a note via the contact link and I'll send you one (while stocks last).
Update - Shipping to Australia only!