Slide the new AirPort card into the slot until its firmly seated.

Reconnect the AirPort cable to the optical drive panel.

Reattach the optical drive panel and restart the eMac.

To configure the AirPort card, go under the Apple in the upper left hand corner to System Preferences - Network. The AirPort option should be on the left hand window. Select it.

It should set up on its own. If not hit the "Assist Me" box on the bottom of the page.