There are some live players that figured out how to use a glitch to get COD2 working much better on xbox live. You can select the match specifics, and lag is much improved.

Here are the directions:

First you need two people with COD2, xbox live, and an xbox 360 each.

Player one needs to go to COD2 system link and create a game (pick the level and set the times (30, 45, or 60mins) now just stay at the screen don’t start the game yet.

Player two starts a different game, maybe an arcade game so you don’t have to change disks, and then player two invites player one to his arcade game.

Player one accepts the invite but when it warns that you will log out of COD2, click no.

Now you should be the host of the game and it will be set to the specifics you had set.

Xbox.com Forum Thread
A video to help you understand what to do.