Steve:
You may do what you want using either a LIST BOX or a COMBO BOX in your form. Both controls will show a selectable dropdown menu with list of values from the ‘foreign’ table (i.e. the MethodOfPayment table).
But note the difference: a LIST BOX usually is setup to write the ID number (PK) of the chosen item as a foreign key (FK) in the current row of your Payments table, whereas a COMBO BOX will simply write the value of the choice (i.e. the payment method chosen) into the selected row of the Payments table. See THIS THREAD for more info (especially the post by DACM).