Lets go step by step.
How to convert existing ModLoader mods into native mods
First of all, you need your mod. Mods are like structured something like this, depending on which file they load :
\---Mod
\---maps
\---mp
\---gametypes
1) Just take everything from maps onwards, so you should be left with
\---maps
\---mp
\---gametypes
2) Now use a compression tool and zip the folder up, maintaining the original folder structure.
3) Rename the extension to .iwd.
Congratulations, you have made the file that is going to be loaded into the game.
How to load the mod
Now to actually loading the mods.
1) Make a new folder in the root of your MW2 folder called "mods"
2) In the "mods" folder, make a new folder with the name of your mod, for example "MyMod"
3) In your mod folder, place the .iwd file you made earlier into the folder. The .iwd can be named anything.
At this point you should have a folder structure like this :
\---Modern Warfare 2
\---mods
\---modname
4) Run the game
5) Type in fs_game mods/MODNAMEHERE . Note that MODNAMEHERE is the name of the folder you created in "mods".
6) Type in vid_restart and start a game, the mod should have loaded if everything was done correctly.
Taken from alterIW.net