Once you get the card installed in the slot, fire up Apple System profiler and see whether it is recognized, and what it shows for information.
If it is not a common part like Realtek 8139 or 8169, you will need their driver. After you download the driver, it seems to unpack into a folder named "Driver". There is a Mac OS X folder inside, which includes a ReadMe and the software.
What Mac are you installing this into? The Mirrored Drive Doors G4 HAS Gigabit Ethernet.
Message was edited by: Grant Bennet-Alder