Your ISP should have provided you with both a CD that auto configures your connection, and a document with your username and password included.
Thank you for the response.
I have set up the wireless router and can connect to the Internet via a PC running XP (wirelessly through the network!!) - an identical set up on a different PC (running Vista Home) presents a login screen asking for a UserName and Password. The Vista PC has connected to the Local Network, but will not allow access to the Internet!!
How are you trying to connect to the network in Vista? Through the network icon in the system tray? It should only be asking for a password to get on the internet, and no username, unless you are trying to access a shared drive or other network resource.
I take it you are sure you left your WIFI network unsecured? Are you sure your XP machine didn't long ago provide a password to connect the first time and now it connects automatically?
Any secured WIFI network will require a password to connect.
If your network is not secured then are you sure the Vista machine is not attempting to connect to a neighbor's network?
Log into your router and check your wifi security settings. If you do not have it secured then secure it, preferably with WPA, supply the password and then try to connect via Vista machine. This will of course knock out the XP machine too until you reconnect with the new password.
Once you connect with the password the first time if you 'save the network' you will not have to enter the password again.