I'm not really familiar with the 3Com '900' series cards are you sure you have an ISA card, from what I've found searching the 900 Combo is a pci card?

as root in a console or terminal window use the following command:

modprobe 3c59x

post back any error messages.

If in fact you have an ISA card I would expect it to be a 3c509 which has to be set up in ISA mode not plug-and-play mode to work in linux.

rock