Limewire offers an option on connections with "Freeloaders". I think Bearshare also can block freeloaders.
Another thought. If a connection is "high speed" even if not sharing wouldn't it be better used "deeper' than My Modem connection with lots of shared files. I can only give you connection to two servants where the high speed could give you many. Limewire sets me up for two outbounds and 0 inbound's, this puts modems on the fringe of the network.
[This message has been edited by lightstone (edited 03-03-2001).]