Won't connect to internet at local library

I can connect to the internet via wireless anywhere, home, school, at a friends house but I can't connect to the WiFi at my local library. I used to be able to but now it just won't get internet, it just assigns itself an IP address and leaves it at that. I know it's not an issue with Mac because when this happened for the second time there was a man next to me online on his MacBook. I've used the internet there on a 2005 iBook G4 which was also running Leopard. I've also been there with a Sony running Linux and Windows without issue. I've also reinstalled OS X Leopard but it still won't connect to the internet, just the local network.