I've installed airport cards in my iMac G4 and my iBook G3-900 and it was just a case of removing the bottom plate on the iMac and clicking the card into place, and on the iBook you just push two levers at the back of the keyboard to lift it up, raise the metal holding bracket and put the airport card in, lower the bracket again and you're done.
Are you sure you followed the installation instructions properly?
Sounds like you tried to install the card by removing the case?
The instructions for installing an aitport card in a Titanium Powerbook G4 are here:-
http://manuals.info.apple.com/Apple_Support_Area/Manuals/powerbooks/0342010.Book.PDF(page 67)
[Edit] You should just remove the bottom cover and the airport card slot is right there underneath.
You shouldn't need to remove drives or file anything away, or cut away any shielding.
I've owned 3 macs now and my next one will be the new 15" Powerbook. Only problem I've had was when my iMac had a dodgy hard drive. One call to Apple had the machine picked up the next day and it was returned the day after with a new hard drive fitted and everything re-installed. No hassle whatsoever.
I wouldn't go back to Wintel now if you paid me.
