Suddenly unable to connect to wireless network:
This morning I connected to my wireless network (DSL 2WIRE modem/router) with no problem. This afternoon I returned and Airport refused to connect, giving me the error message, "Airport is unable to connect to the wireless network*" The network shows up as being available, but when I attempt to connect, it wont. (I didn't make any changes or install any programs this morning).
Here's what I've done:
 Restarted the router
 Repaired permissions
 Deleted the network's entry in Keychain Access
 Re-entered my WEP code (assuring it is in correctly; I've tried both with the "$" and without)
 Used interface robustness and without.
 Attempted to join the network from the System Preferences>Network.Airport route.
 Created a new account and tried connecting.
Other tidbits of information:
 Another MacBook in the house connects to the network with no problem.
 My MacBook can connect to another (unsecured) network that I can "see" in my house.
So, it would seem my Airport card is working okay.