Some more options...
Save the file as an add (*.xla). But don't use personal.xla as the file
name--if you do that, then you may collide with a user's own personal.xla file.
(Excel can only have one file open with that name.)
Save it to a network drive and mark it readonly (using windows explorer).
Have the users do:
tools|addins and browse to that location. I'd suggest that they use the UNC
path (instead of the Mapped drive) to locate the addin.
You'll have to give the users some way to access the subroutines. (Macros in
..xla's don't show up in the tools|macro|macros dialog.)
For additions to the worksheet menu bar, I really like the way John Walkenbach
does it in his menumaker workbook:
http://j-walk.com/ss/excel/tips/tip53.htm
Here's how I do it when I want a toolbar:
http://www.contextures.com/xlToolbar02.html
(from Debra Dalgleish's site)