Yeah, the default popup window specified by the "AppointmentFormPath" is pretty old school, isn't it?  When we first implemented the out-of-the-box WebSchedule model, we were disappointed as well.

When we recently evaluated the possibility of implementing an AJAX popup in the context of the WebSchedule controls, we came to the conclusion that it would be more work than we want to take on, based on other higher priorities.  Maybe by the time we revisit this issue, Infragistics will have a more modern (dialog) model in place.