The format of the ethernet parameter is as follows:
ether=irq,baseaddr,memstart,memend
This shouldn't be necessary for many cards, however. An example would look like:
ether=11,0x360
Note: The last two parameters can be left out most (if not all) of the time. Also, linux will only recognize the first ethernet card in a system. To get it to see two, you must use a parameter like:
boot: linux ether=0,0,eth1
For more information on this, see the Multiple-Ethernet mini HOWTO.