therboot does not (yet) offer support for PCMCIA cards.
The tricky part is to initialize the PCMCIA controller. Before a PCMCIA Network Interface Card can be configured, has that device be setup.
Source code for how to talk to @@yenta@@ chips is available in the Linux kernel.
In other words:
This challenge waits for those who looking for an interresting problem ( and / or glory
If you are http://www.ltsp.org LTSP user, look at the LTSP “wireless” packages at http://sourceforge.net/project/showfiles.php?group_id=17723
That package contains a floppy image that can be used to boot off wireless or wirebound PCMCIA network cards (probably other wireless [=NICs=] as well).