I installed an Airport card in my Power Mac a couple of days ago and just noticed I forgot to set it to use OpenDNS in my network preferences. I just assumed the DNS servers would carry over from the ethernet settings. So don't forget to update!
OpenDNS, by the way, are freely available DNS servers that are very handy in case you're having trouble with your ISP's default servers (it wouldn't be anyone like Earthlink or anything). Just enter these two addresses in your DNS Server field in Network Preferences --> Airport --> TCP/IP:
You're good to go!