Just a quick check list (going from experience with BT):
Make sure that under the connection settings of IE it is set to never dial a connection.
(if you are prompted to dial up each time this could be it)
Go though the internet connection wizard and tell it to connect using LAN

If they have provided you with IP settings then, they most likely gave you a dns server IP?
If so pinging this IP willl be a good test as it is the one IP you should know for sure without having to use DNS.