Must you have the modem on the client end? Or can you put it on the server end? You may want to try one of the USB or Serial to TCP/IP converter boxes instead, as people have had great success with these.
Considering awarding points if this is of use
Rodos
{size:10px}{color:gray}Consider the use of the helpful or correct buttons to award points.
Blog: http://rodos.haywood.org/{color}{size}
