the ISP will be the one to recommend a proper ethernet modem, which can handle the many simultaneous connections needed for filesharing.
If you are stuck with the USB modem, then reduce the number of simultaneous connections LimeWire will attempt. Here are some ways to do that if you really want to cripple LW:
--check "disable ultrapeer" in the options. UP connects to 60+ hosts
-Use the Free, rather than Pro version. The Free uses 2 fewer connections in Leaf mode. Poster et voilą knows ways to get Pro or the CVS version of LW to use fewer connections (you can send him a PM)
--search and download only one file at a time (or try a few until the modem chokes again)
--clean out your incomplete folder, so all those files stop trying to connect at startup and later intervals
--turn off Partial File Sharing
gad--what a waste of a good connection. Really--get your ISP to recommend a decent modem