Internet issues

My friend has a PB and Safari (nor IE) will connect to the internet, but AIM works. Any possible reasons or solutions?

are you connected via airport?
what kind of internet service do you have?

It is at a college dorm. Other computers around, however, are connecting without problems. It seems that it works after a restart, but after some time of inactivity the internet connection fails to work. I suppose it may be a problem with the network and not the computer but I just wanted to see what some other people thought.