I assume you are UK. If so, you have to get a MAC code to stop with your present ISP. They will then clear the line. You provide your MAC code to the new ISP who then set you up.

Broadband is linked to your telephone number and only one ISP can be used. Thats as I understand it.

Never tried it, but I would have thought you can have one person using Broadband, and the other using the telephone part for 56K dial up. After all you can use your telephone at the same time as your broadband. However if that was possible, I would be surprised if you could use wireless for both machines - I would have thought that would create major confusion. The person using broadband could use the wireless modem/router and the other plugging there modem connected to the PC into the telephone part of the telephone line. Obviously no telephone at that point.

I will probably get shot down in flames now :-)

Hope you get it sorted, and would be interested in the result. An interesting thread.