You can make a combo box on a tool bar, but you have to general make your
won custom menu bar (that is easy).
The real problem is that a combo box is not deigned for very many entries.
Further, when you use a menu bar, there is no provision to simply "load up"
the combo box with its data (you have to write code). So, if you are talking
about something with only 100 or so entries, then yes..I would consider a
combo box in the menu bar. However, if anything beyond a 100 or so...then it
would be a bad user interface (too many thing to select),a and also a bad
coding/resource issue (you have to pre-load the combo box with the data via
code...and it will take memory, and resources beyond what would be prudent).
Likely, you should just put the combo box high up in the forms "header"
area...and then you can use a ms-access combo..and not a the VERY limited
menu bar combo.
While I create lots of menu bars...to add a combo box..you do need to use
code.
There is some examples here:
http://www.microsoft.com/Accessdev/articles/bapp97/chapters/ba01_6.htm