I had the same problem with 3 of my iBooks too! Unfortunately, the problem is at the connection between the Airport card connector and the logic board. Apple did not do a good job soldering the connector for the Airport card to the logic board, and it will cause a kernel panic. Replacing the Airport card will not make a difference. However, this is what you can do to make your Airport work again:
1. Put your Airport Card back into the iBook. Attach 2 wooden floor protectors (you can buy them from IKEA) on top of the Airport Card.
2. Reattach the grey plastic brace that spans across the Airport card and ends at the heat sink. Screw the brace down as much as you can. You want a lot of pressure on the Airport card.
3. Put your computer back together and enjoy!