the tip on Point A, "Customizing Toolbars and Button Bitmaps" explains it best. Here's the link:
http://pointa.autodesk.com/local/eng/portal/bucket_viewer.jsp?beanName=Tips+%26+Techniques&tipID=3540&from=box&ismod=true
Basically, you have to save it with a name you give it, in the folder you want. Then you have to
manually edit the .mns file, find the menu line for the toolbar, and replace the "iconxxx" with your
name and full path.
I was going insane trying to save menus & bitmaps on the file server for for all of us to use, until
I found this tip. No more smiley faces for me!