On AlterIWNet, when you hit Play on the main screen does it allow you to go through? If your banned it should just keep trying to connect.
If it is that you should go on alteriw.net and search the forums for your IP ( www.whatismyip.com ). There is a program on there to find your XUID, but you can also in the Main/games_mp.txt file in your Modern Warfare 2 directory and search your name (control+f). It should be right next to it. You can search the cheaters forum for that too.