You can do this with a data validation dropdown list and programming.
There's an example he

http://www.contextures.com/excelfiles.html

Under Data Validation, look for 'DV0017 - Select Multiple Items from
Dropdown List'


Jenty56 wrote:
I've created a drop-down box in a spreadsheet and want to know if it's
possible to select more than one entry at once.

I have a list of manufacturers (i.e., Sony, Panasonic and NEC) with the
intention of having our resellers choose the manufacturers they use. For
research purposes, it is important that we capture the entire breadth of
their selection.

Suggestions?


--
Debra Dalgleish
Contextures
http://www.contextures.com/tiptech.html