I just asked because on the nintendo wii site it says:
"Nintendo offers a free and fun online service for all Wii users. In order to connect your Wii online however, you must meet the following requirements:
You must have an existing broadband internet connection, such as Cable or DSL. If you are not sure if your internet connection is broadband or not, please consult your Internet Service Provider.
A compatible Internet Service Provider (ISP). While most services are compatible with the Wii, some ISPs do not allow additional devices to be connected to a network. Consult your ISP for more information."
But others have now told me it's ok so thanks for the replies.