Thanks to everyone's help I finally got it working.  Here are some of
the issues that had to be resolved

The mouse problem was using the PS/2 driver in X.  Mostly people
said to use busmouse but if you have wscons installed you need to
use the wsmouse protocol.  Here's the relevant section.

Section "Pointer"
    Protocol    "wsmouse"
    Device      "/dev/wsmouse0"

    Emulate3Buttons
    Emulate3Timeout 50
EndSection

I was running the VGA16 server instead of SVGA because the SVGA one
wouldn't even work at 640 x 480.  It seems that 800 x 600 only works
with the SVGA server.  Now I have the SVGA server installed and it
works at 800 x 600 but I can't make 640 x 480 work.  I'll live with
that problem.  :-)

Soren S. Jorvang suggested using a Chipset line of "tgui96xx".  That
didn't work at all but it led me to remove the generic chipset line
and let the driver work it out.  That's when I started getting some
different screen behaviour and tweaking the mode line made it work.
Here are the Monitor and Device sections.

Section "Monitor"
    Identifier  "ThinkPad"
    VendorName  "IBM"
    ModelName   "560"
    
    HorizSync   20-70
    VertRefresh 55-90
    ModeLine "800x600" 50      800 856  976 1040   600 637 643 666 +hsync +vsync
EndSection

Section "Device"
    Identifier  "svga"
    VendorName  "IBM"
    BoardName   "9385"
    ClockChip   "tgui"
    VideoRam    1024
EndSection

And, for completeness, here is the Screen section.

Section "Screen"
    Driver      "svga"
    Device      "GUI"
    Monitor     "ThinkPad"
    #Subsection  "Display"
        #Depth       8
        #Modes       "800x600"
    #EndSubsection
    Subsection "Display" 
        Depth       16
        Modes       "800x600"                     
    EndSubsection
EndSection


Note that the 8 bit depth mode works but I commented it out so I always use
the 16 bit colour mode.

Again, thanks to everyone who made suggestions.

-- 
D'Arcy J.M. Cain <darcy@{druid|vex}.net>   |  Democracy is three wolves
http://www.druid.net/darcy/                |  and a sheep voting on
+1 416 424 2871     (DoD#0082)    (eNTP)   |  what's for dinner.