External Modem installation

Ubuntu 6.06 is successfully installed on my Dell Dimension. However the installed internal 56K modem does not appear to be supported so an old Zoom V34 EXTERNAL modem on serial port was substituted. Apparently it is recognized by Linux but when my ISP (Earthlink claims to support Linux and V34 protocol) is dialed no connection is made. The website for Zoom modem talks only to experienced Linux users but not for newbies like me. What else can i do to continue testing this config ? Newbie Bob