Tools needed
Modio
4GB USB
MW2
Xbox360

Ok to start off put ur USB in ur Xbox then configure the USB
Then start mw2
Go to campaign start a new one and make shur u click USB as storage
Then take USB out Xbox put in computer
Start up Modio go to explore device
Click mw2 save games
Right click on ur save game click open in rehasher
Click mod file then u can put any mods
Then say and rehash and resign
Save to device
Put USB back in Xbox
Start up mw2
When it ask u to pick storage device click USB
Start campaign there u go