you have the external bios switch board, right? Has an led glowing. And has bios select/chip off/write protect options.
Your chip is supposed to look like this:
http://www.xbox-scene.com/modchips/x..._pictures.html
You can either have a 1mb bios or a 512k bios on it. The x2 4983 are multi, so it will work in a 1.1 xbox as well as a 1.0.