Memory And Link
In order to trade your game backups with friends, who also own Xboxes, you'll need a memory card. All of the accessory manufacturers make them. The prices range from $25 for Interact to $35 for Thrustmaster by Microsoft.
The capacity is always 8 MB. That leaves the link cable, which, with a word to the wise, is in fact a stupid, twisted-pair, PC network cable... Gamester offers a nice package.
For $35, the Cortex contains a 8 MB memory card and a link cable, all in all a user-friendly kit.