Seriously? OK. I hope that this helps.
After downloading a mod (ie maps, crosshairs, weapon skins etc)
place the .pk3 file in the mohaa\main directory on your harddrive. (I believe the default directory when installing the game is c:\program files\ea games\mohaa\main If you download the mod and it is in .zip format just extract the .pk3 to the above directory. Keep in mind that you can only have one type of mod (for each weapon, crosshair, hud etc) in the mohaa\main directory ie. one mp40 weapon skin, one grenade skin, one crosshair skin. maps on the other hand, you can have has many has will fit on your harddrive.
one other thing, if you don't see the mod after starting mohaa, try unchecking texture compression which is found in the options menu of mohaa. and lastly here is a link for aa.com map downloads (TM,FFA,RBM,OBJ)
http://www.alliedassault.com/pafiledb/p ... gory&id=10