Here is a guide on getting the files on your already jtagged system and preparing it for hosting MW2 lobbies. Yes, this guide is assuming your system is already jtagged, if you need a guide for that check teh internets.

UPDATED FOR TU4

ALL OFFLINE:
1)Install xexmenu 1.1

2)Run XeXMenu and Create a folder on the root of the drive called "Games" then in that directory create another folder called "MW2" go into that folder and select "Copy DVD"

3)Replace original Files with modded ones in MW2 Directory(Make backups of originals first!)
the modded code_post_gfx_mp.ff I use can be found here:
code_post_gfx_mp.ff Thanks to coolshrimp

TU4 default_mp.xex can be found here:
default_mp.xex Thanks to XiX

The DPAD UP challenge mod can be found here:
patch_mp.ff Thanks to swifteh

**MAKE SURE YOU OVERWRITE THE CORRECT code_post_gfx_mp.ff and NOT code_post_gfx.ff THE FILENAMES ARE SO CLOSE AND THIS IS USUALLY HOW YOU GET THE DREADED DISK READ ERROR!*** the patch_mp.ff files goes in the same directory as the other 2 files no overwrite needed, unless you already have another patch_mp.ff in there.

4) Get the latest Title Updates from this site XBOX 360 Update Center and place them in "Cache" folder found on the root of the HDD, copy the files over with xexmenu.

5)Load up xexmenu and run MW2 from the menu, then go into Multiplayer and at that point you can connect to Live.

NOTE: For match hosting you want it to be Private>Free-for-All>Any Map You Want! See below for coolshrimps configureation for his code post file. For the "DPAD UP challenge mod", for the jtagger you need to switch to tactical but anyone that joins can just press UP on their DPAD. THIS IS NOT MY TUTORIAL IT IS JOHN JACOBSONS FROM HOLYMODS.COM AND IT WAS EDITED BY ME!