oh also worth noting, is something that General 101 & I noticed which is that some of the maps on:
http://h2v.halomaps.org/ don't work correctly with the version of Halo 2 Vista that Cartographer runs on, so be aware of that if you decide to download any customs from there, they may not all show up in the in game custom maps menu -- which you can find if you start your own multiplayer lobby, and hit the right arrow key in the maps list when setting up a custom game. Some of the maps aren't named the same thing in the in game menu as they are named as a file, and even more confusing sometimes at least on H2V.Halomaps -- they will name it something different on the webpage, something different for the filename and something different for the ingame display name for the map. Talk about confusing good grief 0_o
In specific neither Xtreme Climb map works from h2v.halomaps.org