Connecting to Wireless server via Airport

[zigxter]

Every so often my iBook G4 starts acting funny. Airport detects a wireless network and connects to it; I check Networking and I have an IP address and everything but it will not connect to the internet. Safari says it can't detect internet and Terminal doesn't change to "~wireless:". Some times everything falls into place after a short while but some other times I have to try for a while before it works. I can't figure out what's happening.