I am having a problem with a networked iMac which has an Airport card. I just swapped out my Airport Extreme for a Time Capsule, and although I have no problems with the iMac I am using, the other one keeps giving me a message that I am not connected to the internet. This generally happens after it wakes from sleep. The network shows up in the menu, and when I try to connect, it asks for a password, which I enter, and the first couple of attempts to connect give me a message that there was an error joining the network. Eventually it does connect. Am I missing something which needs to be done???
I experienced a similar situation when I upgraded one machine to 10.5. Checking the box to put the password in Keychain solved the problem for me.
Daryl