How to configure cable modem (ethernet output) to DSL Router to Computer?

How do I share my cable modem (with ethernet and usb output) to other computers?
I have a DSL Router and a cable modem and 1 windows xp computer, 1 windows vista computer, 1 windows vista laptop. I tried to connect my modem via USB and share it over LAN, but the modem is like another LAN network so I cant enable both networks… Any solution??????? 🙁