Perhaps, if you could switch the card back in to the iBook, to see.
There is a chance then you could test the card in the eMac, too.
Not sure if the antenna wire into the card was fully pressed in to
make an adequate connection, so these details may help fix it.
A re-install of the OS X should not be required to get an airport
card to be noticed by the system, usually a restart after a card
installation is about all that would be required, plus settings.
As tedious as the compact design of components and tight access
are in these (and later models) no wonder they've about sealed them.
Hopefully the matter is one you can address, and no other wires
are otherwise loose from the hard drive replacement efforts.
Good luck & happy computing! 🙂