I just read a good posting on a blog concerning how to add buttons to the toolbar. The most obvious way is to use the isv.config.xml but this page also explains how to add buttons to the toolbar using javascript. This technique can be expanded to do even more interesting things with the GUI, if needed. Enjoy:

http://www.tconv.com/blogs/crm3tips/2006/03/modifying-standard-toolbars-in.html

Gustaf Westerlund
CRM and SharePoint Consultant

Humandata AB
www.humandata.se