A great app from a fellow MVP here called metaman that does just that!
"BDC Meta Man is the only application that provides the ability to create Application Definitions for the Microsoft Office SharePoint Server 2007 (MOSS) Business Data Catalog (BDC) without writing a line of code. No programming experience is required to take full advantage of the BDC Meta Man. As long as you know how to use a mouse and a keyboard, you can easily generate Application Definitions with BDC Meta Man!"

http://www.bdcmetaman.com/default.aspx