Is it possible to set a drop down combo box so that the valuse are displayed when clicking on the drop down { ] but the values can not be changed, i.e. I would like some thing like the following

    [xxxx[ ] to display [xxxx[ ]
                          xxxxx
                          yyyyy

when clicking on the drop down list but not to be able to change the existing value or do I have to do it as two fields?

TIA for any help.