Well I think I've answered my own question.  I used the WebScheduleInfo ActivityDialogOpening feature to prevent the AppointmentAdd.aspx from loading (using oEvent.cancel = true) so that I can call my completely custom form.  I pass it the Datakey so I can load the data from my own database configuration and the StartDate/Time to handle NEW appointments.

function WebSchedualeInfo1_ActivityDialogOpening(oScheduleInfo, oEvent, oDialog, oActivity)
{
    oEvent.cancel = true; //Cancel default form

    var StartTime = oActivity.getStartDateTime(); //Get Activity start time to pass to custom form
    var key = oActivity.getDataKey();

    window.showModalDialog("fCustomAppointment.aspx?StartTime=" + StartTime + "&Key=" + key);
    window.location.reload();
}
 

Try the following code, it should work.     

  <asp:AccessDataSource
              ID="clinicDataSource"
              runat ="server"
              datafile="~/include/DB/webSchedule2.mdb"
              dataSourceMode = "DataReader"

           SelectCommand = "SELECT * FROM [Activity]"
            >              
            <SelectParameters>
 
            </SelectParameters>
            </asp:AccessDataSource>
           
           
            <asp:GridView
            id="EmployeesGridView"
            runat="server"
            AutoGenerateColumns="True"
            DataSourceid="clinicDataSource"
            visible="false" />

If you're passing the values in a query to the custom dialog page you should be able to bind the dataset in the back code and use the data key, if you made the data key a unquie identifier about the record, to obtain the rest of that record.

I set my datakey to the sql datarow's id. Garuntees that I can use the number to fetch the data from the dataset again.