I assume you know how to insert the listbox itself into the form with the help of the Scout perspective. If not, please say so.
I suggest that you use a LookupCall and an associated LookupService to load the data.
In the list box in your form, simply override
and return the class of your new LookupCall.
For your LookupService, have a look at the AbstractSqlLookupService, where you only need to override "getConfiguredSqlSelect()" to get you started.
The Scout perspective will easily let you create a LookupCall with a LookupService, by right clicking the "LookupCall" folder(in the "shared" part of your project) and choosing the "New LookupCall" option.