Access MVP Garry Robinson has posted a useful article on building custom Access 2007 ribbons using the tool IDBE Ribbon Creator tool from http://www.ribboncreator.de/en/.
You should also checkout an article I wrote in December How Custom Access 2007 Ribbons Work.
I will take this opportunity to promote two free tools I have developed for reviewing custom ribbons that you can download from aadconsulting.com:
These tools providing advanced Office 2007 RibbonX review features. Open any Office 2007 Ribbon XML file in the XML File Reviewer to review an Office Ribbon's full menu hierarchy in a tree-view with all control attributes detailed in an adjacent panel.
The Access 2007 USysRibbons Add-In reviews and previews the custom Ribbons in the USysRibbons table of an Access 2007 database. Extensive reference resources are incorporated into the GUI of both products. Both tools require Access 2007.
The Access Ribbon Review in action (click on the image to enlarge):