It is possible but certainly not easy. The Forms Toolbar combo box does not
return the selected value but rather the index. So you need to use a formula
to show the selected value.
With your combo box hooked to return its value to A1 and the list range in
B1:B10 you would use a formula like
=index(B1:B10, A1)
Since you are using a formula to show the value it would be more than
inconvenient if it got overwritten. You can get around this using the camera
tool as described here but from personal experience it is a bit fussy to make
it work...
http://spreadsheetpage.com/index.php/oddity/the_camera_tool/
Essentailly it allows you to show the value of a cell (the one with the
formula) in another cell. When your users type in the cell they are not
overwritting the formula.