If u are using a dialup modem then telephone line is needed, with modem alone u cant connect
you didnt mentioned how u tried to download , is it by any download manager ????
if u are usrin cable modem and sharing with another computer, and cant download , it means the system ur sharing uses proxy server, if the proxy server supports then find the settings of ur download manger and specify the port no and ip address of the proxy server, if its socks proxy then u have to provoide username and password also, it will solve this
might be ur using server assigned ip address when u connect to the cable modem,
when ur offline u cant use netmeeting, try when online

be more clear with ur questions so that ppl here can answer u quickly