Thanks a lot for your great support, JasonW!
Not to anybody's great surprise the driver does load but is un-loaded immediately due to a ABI-version mis-match. (Sorry, I dit not detect that from skimming over the source code file. At least, I have learned about the importance of ABI-versions.)
For anybody's reference here is the Xorg.0.log:
[ 129.177] (II) LoadModule: "fpit"Seen the sheer age of this software, I do not think that there is anything that can be done (other than re-writing the driver -- which does not look overly hard). So I suggest purging this extension from the repository again.
[ 129.179] (II) Loading /usr/lib/xorg/modules/input/fpit_drv.so
[ 129.181] (II) Module fpit: vendor="X.Org Foundation"
[ 129.181] compiled for 1.12.4, module version = 1.4.0
[ 129.182] Module class: X.Org XInput Driver
[ 129.182] ABI class: X.Org XInput driver, version 16.0
[ 129.182] (EE) module ABI major version (16) doesn't match the server's version (20)
[ 129.182] (II) UnloadModule: "fpit"
[ 129.183] (II) Unloading fpit
[ 129.184] (EE) Failed to load module "fpit" (module requirement mismatch, 0)