Best way to play Call of Duty 4 (or 5) multiplayer from someone else's XBOX 360?

Hi;





I play Call of Duty (CoD) 4: Modern Warfare %26amp; CoD 5: World At War and always play Multiplayer mode online via XBOX Live. It's part of my routine; like 5-6 hours a day :-)





Seriously, I'm traveling to Canada tomorow morning %26amp; my brother in law has an XBOX 360. If I bring the game discs, how can I play from his XBOX 360 in Canada with my guns, classes %26amp; of course, ranking?





I guess what I'm asking really is: For Multiplayer, is your level ranking + custom classes with your customized guns for multiplayer stored with your Gamertag online or is it on my XBOX 360 %26amp; either I need to bring it or get a memory key to copy it.





Speaking of which; are those 512 MB Microsoft XBOX Memory Keys worth it? Enough space? Can I bring back my progress from Canada %26amp; overwrite what I have at home on my XBOX 360?





I'm hoping to hear that this is all stored online with my Gamertag (at least for the multiuser online version), which would make me feel good about the $50 a year I pay Microsoft.Best way to play Call of Duty 4 (or 5) multiplayer from someone else's XBOX 360?
You can recover your gamertag from your Bro's 360. You're going to have to put in some information, email address, password, stuff like that. Then, once you get back, do the same thing on your 360.





:)