I just bought an iBook G4 12 inch combo recently.

Machine Name: iBook G4
Machine Model: PowerBook6,7
CPU Type: PowerPC G4 (1.2)
Number Of CPUs: 1
CPU Speed: 1.33 GHz
L2 Cache (per CPU): 512 KB
Memory: 512 MB
Bus Speed: 133 MHz

I have no problem getting access to the Internet using Airport Wi-Fi at my uncle's house. Strange thing happens when I'm at college trying to use some programs (MSN, ICQ, Yahoo Messenger, Lime Wire, Xfactor, video streaming using Safari,etc...) All of these programs won't work, meaning the programs can't get connected to the Internet. I can only surf using Safari at the college but nothing else. And when I'm back to the hostel, the only programs that can get connected to the Internet are ICQ and Yahoo Messenger. I cannot surf. I've tried Internet Explorer, it's just the same - "...you're not connected to
the Internet..."
In conclusion, my iBook G4 can only surf at the college but nothing else. And back to the hostel, I can only chat using ICQ and Yahoo Messenger, and I can't do anything else that requires Internet connection. I've tried Adium. It doesn't work at the college but it works at the hostel for ICQ and Yahoo only. This strange problem occurs when I'm using Airport Wi-Fi only, I never try Dial-up or others. And the Wi-Fi indicator shows full signal, it says "You are connected to the Network xx. You are connected to the Internet via Airport." And the firewall is off.

When the programs can't get connected to the Internet, the dialog for each program says:

ICQ:
The server has closed the connection

MSN:
You may not be connected to the Internet

Yahoo :
"You have been disconnected from Yahoo Messenger servers."
This error may be due to a loss of your network
connection.Please check your connection to the Internet if
you are having trouble logging on to Messenger.

Safari:
Safari can’t open the page “http://...." You may be not connected to the Internet.

The wireless card I'm using :-
Wireless Card Type: AirPort Extreme
Wireless Card Locale: Worldwide
Wireless Card Firmware Version: 401.2
(3.90.34.0.p13)

I've asked the staff at the college. The proxies all are not blocked. Other students who are using Windows OS can use MSN and chat without having any problems. The staff also told me that I do not need any password to access to the Wi-Fi at college.

I've also tried turning off and on the firewall and also changing the the proxies configuration in the System Preference>Network. Nothing worked.

Everything works fine at my uncle's house. I never changed any network settings since the first day I got my iBook. I just can't get "fully access" to the Internet via Airport at the college and hostel. This is so strange.

Hope someone can help. Thanks a lot.