Implement the "add employee" option, and the "change salary" option. Adding an employee should pop up a window for entering the name, start date, and salary of the employee. Changing the salary should pop up a window for entering the new salary and the date that the change takes place. Both of these options will be like the time-card option, i.e. you will have to make a new ApplicationModel for the window and define the window's layout using the VisualWorks canvas tool. You'll need to write an "interface opening" class method so that you can parameterize the ApplicationModel with an object (probably the payroll system for adding an employee, and an employee for changing the salary). Most of the work in the new ApplicationModel will come in the "accept" method, which will cause one window to add an employee, and the other to create a transaction to change its salary. There will have to be methods in the PayrollSystemInterface that starts up the ApplicationModel. TimecardApplication does all these things, too, so you can use it as an example.
Make some windows to handle the "inspect paycheck", "print paychecks", and "post paychecks" options. Once you say "compute paychecks" the payroll system will create a list of paychecks. The "inspect paycheck" option should give you a list of them and let you look at each one. The "print paychecks" option should ask you for a file name and write something out to it. Doing this right would require knowing the format of the checks, and we don't have any real checks, so don't worry too much about it. Saying "post paychecks" should post them and clear the list. Check PayrollSystem to see what methods it has in the "actions" protocol. In some cases, all you have to do is to call existing methods.