I have found the quickest way to get this achievement is to go into muti-player and select custom games, then select Halo 2 classic mode as there is hardly any loading on the old maps. You can get each game done in around 20 seconds by yourself, be sure to end your game as if you quit out it will not count. At the title screen press b to go back and then start another game. This will stack with all the other win/games played achievements. I won't be surprised if this gets patched soon, so get them games in.