(Consider this an FYI on how I fixed this problem)

The Linux PCMCIA package has a driver, named xirc2ps_cs, for
many Xircom cards.  There is, however a (known) problem in
that it may not work properly work with autosensing cards--
for instance, my Xircom CE3B-100 works correctly in 100BaseT
mode, but not 10BaseT mode.

While trying to find out more about what the problem is, I
visited the Linux PCMCIA web page, and discovered a forum
where someone had asked a question concerning a problem very
similiar to mine; this person was told about a development
release, dated November 4th, 1999 (I think of 3.1.4), that
seemed to correct the issue.

Rather than install the development snapshot, I grabbed it
and back-ported the logic changes to clients/xirc2ps_cs.c
and rebuild the kernel RPM.  This seems to have solved my
problem.  I'll submit the patch I generated shortly...