I have never used the Airport cards that have come with any of my Macs.
I have had better luck with the earlier drivers for third party cards.
And I still use a hardwired connection to my router when it can be made.
That still provides the best bandwidth.

Also I have a really unusual Netgear WNCE2001 Universal Wifi adapter on my iBook (a solution David suggested - thanks again Dave). That thing will connect virtually anything to my router.