You may find Data|Validation a bit easier than a combobox.

Debra Dalgleish has some notes at:
http://www.contextures.com/xlDataVal01.html

But if you used a combobox from the control toolbox toolbar, you can assign it a
linked cell to retrieve the value in the combobox.

If you used a dropdown from the Forms toolbar, then you'll need a linked cell to
return the index into the list and another cell containing a formula that
retrieves that value in the list:

=if(a1="","",index(a2:a99,a1))

If the list is in A2:A99 and the linked cell is A1.