NumLock on the keyboard of IBM T40 Laptop does not work (for info: NumLk shares
the key with ScrLk and should be reachable in combination with Shift-Key)
(on external usb-keyboard NumLock-Key works).

It can be fixed in /etc/X11/Xmodmap :
keycode 77 = Num_Lock


Here the output of "xev" before modification of Xmodmap:
------
KeyPress event, serial 27, synthetic NO, window 0x3000001,
    root 0x40, subw 0x0, time 53000, (264,112), root:(942,144),
    state 0x0, keycode 50 (keysym 0xffe1, Shift_L), same_screen YES,
    XLookupString gives 0 bytes:
    XmbLookupString gives 0 bytes:
    XFilterEvent returns: False

KeyPress event, serial 30, synthetic NO, window 0x3000001,
    root 0x40, subw 0x0, time 53215, (264,112), root:(942,144),
    state 0x1, keycode 77 (keysym 0xfef9, Pointer_EnableKeys), same_screen YES,
    XLookupString gives 0 bytes:
    XmbLookupString gives 0 bytes:
    XFilterEvent returns: False

KeyRelease event, serial 30, synthetic NO, window 0x3000001,
    root 0x40, subw 0x0, time 53326, (264,112), root:(942,144),
    state 0x1, keycode 77 (keysym 0xfef9, Pointer_EnableKeys), same_screen YES,
    XLookupString gives 0 bytes:

KeyRelease event, serial 30, synthetic NO, window 0x3000001,
    root 0x40, subw 0x0, time 53573, (264,112), root:(942,144),
    state 0x1, keycode 50 (keysym 0xffe1, Shift_L), same_screen YES,
    XLookupString gives 0 bytes: