Dial up connection over Broadband-Using VOIP & Asterisk?

I need my computer to use its broadband connection to connect with a dial up provider. I am assuming this will be done over VOIP and many people mentioned asterisk as a possible solution. I need the computer or at least the browser to use the connection of the dial up not the broadband when it connects to websites.(i need the ip address of the dial up) I don't currently use a VOIP provider and would rather use a free solution. I am open to all and any ideas/methods on how to get this done.