Can you have both bluetooth and airport card in computer
if both card are installed will one
interfere with the other?
Apple has a couple of knowledge base articles that deal with the subject:
The second article specifically says that in the Macbook Air, using multiple Bluetooth devices can reduce the transfer rate of Airport networks. One of their suggestions is to use the 5 GHz 802.11 network instead of the 2.4 GHz network (an option I believe is only possible with the 802.11n Airport machines).
The first article mentions the possibility of Bluetooth/Airport interference without specifying computer models. But it offers the same kind of advice -- such as using the 5 GHz channel and reducing the number of active Bluetooth devices.