Are you asking how to do this for a set field of the 20, or are you asking how to do this for ANY field of the 20?
If for a set field, use the method suggested by FirstandGoal4 and Qu1ncy.
If you want the users to be able to query any field in the table, here is one approach you could try.
1. Create an unbound form with two combo boxes, an OK button and a Cancel button on it
2. For the first combo box, set its Row Source to a value list of the name of every field in your table.
3. For the second combo box, use a SQL string to set the Row Source to all the values of the field chosen in the first combo box. This string would be run from the On Change event of the first combo box.
4. In the On Click code of the OK button, run a SQL string to run the query, setting a WHERE clause along the lines of "WHERE [SelectedField] = [Selected Value]".
This should then work for any value in any field within the table. If there are too many values to add to the second combo box, try using a textbox that the user can directly enter a value in.
HTH
Lightning