I followed your guidance and that helped, thanks!
The kernel upgrade seemed to go smoothly and the udev error is now gone, as are the errors about being unable to open devices. I used "aptitude install kernel-image-2.6-686" and "aptitude install linux-kernel-headers", though apparently I already had the headers. It took me quite a bit of web surfing to figure out what architecture my computer has (Compaq nc6000 with Pentium M processor), but I eventually found info on wikipedia indicating that a Pentium M is a 686 architecture. (Shouldn't there be an easier way to determine one's architecture?)
HOWEVER, I then got a bunch of "Could not init font path element" errors, culminating with a Fatal Server error from X: "could not open default font 'fixed'". I searched the debian packages for fonts, took a guess at installing the "xfonts-75dpi" and "xfonts-base" packages, and now it works! Hallelujah!!!
Thanks very much for your help!