Hi,
Hate to point to 'the usual suspect' but I had problems with Miami not recognising my 3c589 when I had a power shortage. Are you running other devices, for example a hard drive and/or accelerator?
If it is a pwer issue you may find you have the same problem with your serial port also.
May be something else entirely, but this is the problem I had.
PS - The only thing I installed (above os3.9) was the 3c589 installation package, which you've already got. This installs the driver in devs:networks, so yes - you are right to put networks/3c589.device into miami.
EDIT<<<>>>
-my mistake, it is required.
Prepcard will NOT recognise this card - the prepcard utility is only for installing memory cards into the pcmcia, and configuring them.
All you need to do is point miami to the driver - no extra utilities, no extra libraries.
Try disconnecting something power hungry (eg accelerator) and see if miami picks it up then. IF you can, try the card on a laptop aswell to make sure you are not wasting your time.
Good luck.