I am no means an expert, but some networks only let you browse the INTRANET not INTERNET, so this could explain why you cant get www.
Usually if you have entered the username and password correct then the www. needs no configuration.
If you get the username and password wrong, it allow none or limited access dependant upon the server settings they are using.
So, check you have the right log in details, then check the network is connected to the internet.
I have never had any problems connecting to www. on my PDA on a wireless network, its just as easy as if it was a laptop....