Ok. Someone suggested that I should set the modem in pure bridged mode with dhcp server disabled. Then set up a pppoe connection on the computer with your IS username/password. Set the pppoe and the vpn connection to auto redial if line is dropped. In the vpn choose the dial this connection first and choose the IS. Also, internet explorer (Tools ->Internet Options->Connection) I first chose "never dial a connection", then for both the IS and VPN, in the same screen, I went
properties->advanced. There I de-selected "Disconnect when connection may no longer be needed" and have had only infrequent disconnections since. In the rare event of the line dropping, it is automatically redialed, so torrents can continue. The modem, as I have it, usually re-assignes your computer a new ip after certain periods, but this can also be turned off.
Hope that helps