I have a list box and am able to populate the list with values from a master file.
What if i dont have a master file but use SQL pass throughs in my application and need to add some more logic to arrive at the values? Can i use a procedure in this case to populate values/

You can use a procedure. Just create a procedure that returns two columns of data: the first one will be the value that is passed to the called procedure for the report, the second will be what actually appears in the listbox. You must also set the procedure to return xml:

ON TABLE PCHOLD FORMAT XML

In the html painter, where you normally choose the Data Source for your dynamic values, choose the 'Procedure' option and then choose the source for it.

There are some other ways if you are wanting to do this all in code. I can send you an example of that if you need it.