[Necrology]

on AlliedAssault.com look at the left
under Community press on Mods n Skins
there press on whatever you want (human skin, gun skins, mod, maps etc etc etc)
when you finally reach to the specific thing you wish to download just press on it
there you can see screenshots, rate it, and ofcourse download it
now press the download file button
it will now go to filefront the place that hosts the files
now there are some few options
press on "Download directly from FileFront.com", than save it to where ever you want
now its ususaly in zip format so you need to have winzip
(if you dont go to http://www.winzip.com)
now in the zip, you will find a pk3 file, mark that file, press extract from the manu above, go to your mohaa directory, there to the "main" folder,
(c:\program files\ea games\mohaa\main, ofcourse you might have a diffrent path)
and thats it.. you got it installed
I cant see how anyone can be more specific