Project Server 2007 developer can use PSI to read global calender.  Here is the example how to read global calender with PSI:

CalendarDataSet cal = ProjectServer.wsCalendar.ReadCalendars(GetByNameFilter(Name), false);

private string GetByUIDFilter(Guid UID)

{

    CalendarDataSet cal = new CalendarDataSet();

    Filter f = new Filter();

    f.FilterTableName = cal.Calendars.TableName;

    f.Fields.Add(new PSLibrary.Filter.Field(cal.Calendars.CAL_UIDColumn.ColumnName);

    foreach (DataColumn c in cal.CalendarExceptions.Columns)

    {

        f.Fields.Add(new PSLibrary.Filter.Field(c.Table.TableName, c.ColumnName));

    }

    f.Criteria = new PSLibrary.Filter.FieldOperator(PSLibrary.Filter.FieldOperationType.Equal,

        cal.Calendars.CAL_UIDColumn.ColumnName, UID);

    return f.GetXml();

}