I strongly suspect that this can be made to work with modern X without any programming
required, but a lot more internet research.
I think the statement that "serial wacom tablets are no longer supported" may
mean that the support has been removed from the X-Windows driver, but there is a different
driver that will get it to work (maybe a linux wacom kernel module?)
When I was wandering around, I found more recent reference to "ISD-V4" drivers
that may be what you need.
Probably finding a forum with more wacom-driver experts would be useful. Maybe posting an
"issue" in the github would find you somebody helpful.
Since Debian was mentioned, I did a little grepping of my downloaded-debian-archive and I
have xserver-xorg-input-wacom version 0.7.9.3-2 for Lenny (Debian5) and version 0.34.0 for
stretch (Debian v9).
It's definitely possible to run old Debian X packages on an otherwise-modern Debian
install (or one that started old and has been selectively upgraded). You could poke
around
http://archive.debian.org/ and grab old versions of the packages.
Or maybe this Thinkpad is too old to be worth all that effort...