If you want to dropdown list a set of items and be able to add your own item, then:
To the right of your sheet build a list one item per row in one column. Click the column ID to highlight the column, then use:
Insert-Name-Define then name your list.
Click the cell you want the list in, then:
Data-Validation-Settings (select "List" from Allow) in "Source" add =your list name, Like: =myList
Then copy the cell you just put the dropdown list in and highlight the other cells you want the list in and hit special paste-validation.
Now when a cell with your dropdown is selected, it grows a dropdown arrow, which when clicked returns your selection list.
To limit the selection to only the values in your list:
Data-validation-Settings
Allow: List
Check: Ignore blank
Check: In-Cell dropdown
Source: =$AA:$AA (this is the column "myList" is in.
Then:
Tab to Error Alert
Check: Show
Style: Stop
Title: Error!
Error Message: Only select from the dropdown list!
Now the user can put a wrong entery in the cell but they cannot move from the cell without an Error Box Message and the options to fix or erase their entery or start over.
Hope this helps. JSW