Depends on your service plan. Did your ISP say you need a specific IP address? A username and password to log in?
If you answered "No," then you're good to go. It will happen automatically, provided your Ethernet card is supported (and 99% of them are).
With most major ISPs, all you need is the cable modem, and possibly a router if you want broadband access for multiple PCs on the same line. Just plug your Debian box into the router and everything should happen automatically. In fact, if you have broadband, you might as well just download the 150MB net-install disk image, and have the installer do what little configuration there is for you.