Sue,

The loRegisterCustomer.createSale is not expecting a string but a property returned from SaleType.

E.g.
loRegisterCustomer.createSale(loRegisterCustomer.SaleType.PayMonthly);

This is why I can't see how it's possible in FoxPro as you do not have the necessary visibilty of all the other object's that you get with .net/java etc.