It has been awhile but you only really need 2 things to setup xbox live for the original xbox.
1. A broadband connection
2. A credit card
After you plug in the ethernet cable into the back of your xbox from your router, everything else can be setup using the xbox menu settings. They'll ask you to input a credit card number at some point, but it should be pretty simple.
I'm getting a bit confused on how to set up xbox live from all the websites for an xbox. What do you need to buy and what is optional?