If you are in a University, you should ask the Computer Center to give you an appropriate IP address. When you setup the wireless connection, it is better to manually provide an IP address, rather than allowing the system to automatically search for available address. Otherwise, you will have problem when you restart the laptop.
In addition, you may also ask the Computer Center to help you setup the connection. Basically, in your laptop (Ubuntu), you can either right click the connection icon -> edit connection, or go to system -> preference -> network connections. On the wireless tab, select the one you used (remove others) and click Edit, then in IPv4 Settings, select Manual, type in the IP address, gateway, DNS, etc. and in Wireless Security, type in the password. After that, the computer will use the same IP address all the time.
Give me a vote if it helps ;-)