Here a better description of my problem. I hope.

PS/2 Mouse problem 
  
  Xwindows comes up normally but when I move my mouse the cursor
  pointer disappears. It looks as if a lot of mouse pushbutton 1
  events occur.  The hardware recognises the mouse (from
  /var/log/messages): 
   Jan 31 16:06:14 pc08 /netbsd: pms0 at isa0 port 0x60-0x67 irq 12

Configuration:
  DECpc 450d2 MT
  Standard NetBSD-1.0
  Added to GENERICAHA kernel configuration:
	device		pms0	at isa? port "IO_KBD" irq 12
  XFree86 Version 2.0 (X11.5 for NetBSD 0.9)

Probed values (startx >& PROBEDVALUES). I don't know if the /dev/kmem
problem occurs before or after I kill X with Ctrl-Alt-Backspace.
-------------- PROBEDVALUES ----------
XFree86 Version 2.0 / X Window System
(protocol Version 11, revision 0, vendor release 5000)
Operating System: NetBSD 
Configured drivers:
  S3: accelerated server for S3 graphics adaptors (Patchlevel 0)
      mmio_928, s3_generic
Using pccons driver with X support
Xconfig: /usr/X386/lib/X11/Xconfig
(**) stands for supplied, (--) stands for probed/default values
(**) Mouse: type: PS/2, device: /dev/pms0
Warning: The directory "/usr/X386/lib/X11/fonts/Type1/" does not exist.
         Entry deleted from font path.
(**) FontPath set to "/usr/X386/lib/X11/fonts/misc/,/usr/X386/lib/X11/fonts/Speedo/,/usr/X386/lib/X11/fonts/75dpi/"
(--) S3: card type: 386/486 localbus
(--) S3: chipset:   924
(--) S3: chipset driver: s3_generic
(--) S3: videoram:  1024k
(--) S3: clocks:  25.20  28.32  40.00   0.00  50.10  76.90  36.00  44.80
(--) S3: clocks: 129.80 120.30  79.90  31.50 109.90  65.00  74.90  94.50
(--) S3: Maximum allowed dot-clock: 110MHz
(**) S3: Mode "1024x768": mode clock =  75.000, clock used =  74.900
(**) S3: Mode "800x600": mode clock =  40.000, clock used =  40.000
(**) S3: Mode "640x480": mode clock =  31.500, clock used =  31.500
(**) S3: Virtual resolution set to 1024x768
(--) S3: Using a banksize of 64k, line width of 1024
(--) S3: Pixmap cache:
(--) S3: Using 2 128-pixel 4 64-pixel and 8 32-pixel slots
(--) S3: Using 8 pages of 768x255 for font caching
xload: cannot open /dev/kmem
XIO:  fatal IO error 32 (Broken pipe) on X server ":0.0"
      after 1372 requests (1371 known processed) with 182 events remaining.
      The connection was probably broken by a server shutdown or KillClient.
xinit:  connection to X server lost.

waiting for X server to shut down xterm:  fatal IO error 32 (Broken pipe) or KillClient on X server ":0.0"


-------- PROBEDVALUES ---------

--Piet