Download the Cnet device archive from Aminet, and check the compatibilty list..
There`s also a fairly new driver for *some* 3Com cards on Aminet.
Apart from that, you`ll need the PCMCIA reset patch from Aminet (or follow the instructions in the cnet device archive, and do a H/ware patch instead).
When you say "unexpanded A1200", do you mean as in 2Mb Chip RAM, no fast mem, no HD ??
I`d at least get a hard drive..otherwise you`ll be in disk swapping hell !
Also, some extra memory and cpu power would certainly help speed up the network..(the PCMCIA port speed is dependant on CPU power).
It`s possible to get an A1200 networked just using a floppy, but it wouldn`t be pleasant to use.