depending on where you are planning to do business - I have worked for a few consulting engineering firms (mid and large size) that are members of the ACEC. Small firms are typically well represented at functions.
PSMJ publishes many books and newsletters on the business side of the A/E industry. You can download free samples of some of their books and newsletters. I think they have one newsletter that is specifically geared towards small firms. Look on amazon or in libraries for books by Frank Stasiowski...I believe he's the head of PSMJ and writes some down-to-earth business stuff that's geared towards consulting engineers and architects.
Also the AIA has published a series of books called "The Architect's Essentials of..." Lots of good stuff in this series; for example I think their book on "Winning Proposals" is outstanding. In general, look through the online bookstore section of the ACEC (as nackra pointed out) and AIA for business-related publications.
I have heard that the Small Business Adminstration (U.S. Federal Gov't) has some decent material online for general startup and operation of small businesses, but I have not personally checked out this material.
