It depends. The Apple Airport cards are just 802.11b cards, so they will work on most 802.11b networks. Where you usually run into problems is with WEP. I have never tried to do WEP on a Mac, so I don't know what types of encryption they support. If the Mac will only do 64 bit encryption and the network requires 128 bit...
There may be some other issues, but that's all that comes to mind right off. Ask whoever said the user had to switch why they said it.