Hello There

First of all you need to decide what kind of menu you want. You can bypass the 1.14 update for MW2 and continue playing with all the old menus (Elite mossy, hide and seek mods etc...) or you can just update to 1.14 and use a menu where you are more restricted with the mods you can use (Infinity ward patched the old style menus). The problem with bypass is that you can only play with other hackers. If you stay on 1.14 you can play with the normal public.
Once you have made a decision, simply find the patch that suits you the most (Go on google and type in either 1.11 MW2 mod menu, or 1.14 Mod Menu) they hopefully will give you a download link. It should be a .ff file, rename it so it says patch_mp.ff. The next either requires you to use filezilla or a USB, once connected to your ps3,
navigate to: dev_hdd0 > game > BLES00683 > USRDIR
Here you will see the original patch_mp.ff for the game, i recommend making a backup of this incase the mod menu doesn't work, or you don't like it. Simply overwrite the patch_mp.ff and load up MW2 and you will be good to go.