INT 50 - PC Thuis Organizer Shell - DO LINE
        AX = 0007h
        ES:BX -> text string
        CX = string length in bytes (0000h if NUL-terminated)
        DL = FFh to center string, else flush left
        DH = upper left row
        DI = window handle
Return: AX = status
            0000h successful
            FFFFh error
Program: The PC Thuis Organizer Shell was written by John Vanderaart and
          published in the June/July 1990 issue of PC Thuis Power magazine