There are some other ways I think, but this will work:..(well, I hope so)
Download wallpapers HD lite from the appstore, than click the little ''box-with-paper'' icon under the ''get''-button.
It will open a finder-window, click on the ''view-in-rows''-button (to show the files in rows from left to right)
than go left (or ''back") till you see the ''containers''-file.
Above the ''containers''-file is a file called ''application support''. Open that file.
Inside the ''Application support''-file is a file called ''call of duty black ops''
Than go to ''players''.
for the rest go to thid video: http://www.youtube.com/watch?v=uHJN9RsLECw
Go to 01.25.
from that moment you can do what the man..(i suppose)in the video is doing.
(sory for my bad english...i'm dutch)