Installing Debian GNU/Linux testing (Sarge) on Compaq Presario 900US laptop
  ===========================================================================

I booted up the netinstall CD like this:

   (boot prompt): linux26

I had to specify "linux26" because only a 2.6 kernel could recognize
CD-ROM drive after booting.  The default 2.4 kernel couldn't find the
CD-ROM.

I went through the installation procedure as usual.  When I answered
the mouse question, I chose PS/2 (/dev/psaux), and completed the
installation.

Later, X Windows wouldn't start, because it couldn't find a mouse
device file.  The devices "/dev/psaux" and "/dev/input/mice" did not
exist.  So I put

   mousedev
   psmouse proto=bare

into /etc/modules and rebooted.  Afterwards, not only were the right
devices created, but the "proto=bare" made the computer able to
recognize an external PS/2 mouse as well as its built-in TouchPad.
After that, X Windows could start.

(By the way, somewhere during the above I also did

   # apt-get install discover-data
   # apt-get install libdiscover2
   # apt-get install discover

...though it's not clear whether that mattered or not.)

In /etc/X11/XF86Config-4, I changed all mouse devices to use
"/dev/input/mice", although "/dev/psaux" seemed to work too.  I left
the protocols alone; one was "PS/2", another was "ImPS/2".  Since
these were plain old two-button, no-scroll-wheel mice, probably
anything in the "PS/2" family of protocols would work fine.

Configuration of X Windows had some oddness as well.  It never seemed
to respect my choice of 1024x768 as the default resolution, and went
to 800x600 instead.  So in /etc/X11/XF86Config-4, I manually added
"1024x768" to the fronts of the resolution lines in the obvious way
(search for occurrences of "800x600" and you'll see where).  After
that it started up in 1024x768.  

Note that 'dpkg-reconfigure xserver-xfree86' seemed to ask all the
right questions, yet still didn't fix the default resolution, even
though I told it "1024x768".  Go figure.  Editing XF86Config-4 was the
only way I found to fix the resolution.

Lastly, to get sound working I had to install the ALSA sound drivers.
But first, I had to fix my /etc/apt/sources.list file.  For some
reason, the debian package sites listed there were commented out.  I
removed the "#" marks to uncomment them, then did:

   # apt-get update
   # apt-get install alsa

This caused apt-get to suggest some other packages, I think
"alsa-base" and one or two others.  I just followed the suggestions.
After they were installed, I ran 'alsaconf' as root.  I did not run
'amixer' to adjust the volume level, but you may need to do that.

Web pages that were useful during this installation:

No PS/2 mouse devices available:

  http://www.linuks.mine.nu/debian-faq-wiki/OtherHardware

External mouse not working even after TouchPad was:

  http://www.debianplanet.org/node.php?id=1094&cid=13193
  http://www.redhat.com/archives/fedora-test-list/2004-February/msg00717.html

Mice and input devices in general:

  http://kerneltrap.org/node/2199
  http://www.xfree86.org/current/mouse6.html#28

And of course, the ultimate resource:

  irc.freenode.net, channel #debian

Much thanks to Alexander Tait Brotman (abrotman in #debian on
irc.freenode.net) and Micah Anderson for their help.