Dependant Drop Downs

Hi

I have added some dependent dropdowns to my work sheet which work as you go down the list. I am try to:
1) Make it error or give a notification if you make selections down the list (Levels 1 to 4) but then say change the Department from Human Resources to Finance, as the lists have been prepopulated buy Human Resources dependents .i.e. the old value stays in the cell even though the dropdown lists have changed to Finance. So either remove the old values or get Data Validation to popup a message.
2) Remove the underscores ("_") in the selections.

Thanks

Kind regards

C