I have 3 tables with about 25 items in each. I want to create an input form that allows a person to choose a single piece of data from any of those tables and placed into another table.

You can base your combo box on a query that will show a field from all the tables or you can have 3 separate combos each based on one table. In the after update event of the combo(s) you can use something like Me.FieldOnForm = Me.Combo.column(x). I am assuming that you only want on bit of information from the combo(s) and the form is based on the table to get the selected data.