I've had similar PCMCIA related issues with modem card.
When inserted during normal work, the system would crash. When in slot during boot, the system would not boot past the modem initialization. I opened a ticket (01689 in eCS Bugtracker
http://bugs.ecomstation.nl/view.php?id=1689). This issue was caused by missing serial port drivers on systems where there was no serial port. OS/2 was then unable to assign a COM port to modem upon modem initialization.
I do not think that this will be immediately helpful for your problem (my PCMCIA modem is not your PCMCIA network card), I was just surprised to see the same symptoms with you card.
Maybe you should point your investigation on the fact that upon card insertion, OS/2 might have need to initilialize something (probably network-related) that is missing in the current system installation?
Stefan