First I must say I use Photoshop for skinning. You also need a plugin for the file type halo/halo 2 uses, which you can get here. You extract the "dds.8bi" into your Plugins folder of your Adobe Photoshop directory. You're all set to open .dds file types from now on. Make sure you click "No" when you get a prompt that says "Image has MIP maps, Display them with the image?"
In halo 2 there's a different approach to skinning of bitmaps. To save loadi, Bungie decided to make bitmaps and other tags that are used in multiple maps in one map, "Shared.map" for MP, and "Single_player_shared.map" for SP. Also, other bitmaps and tags are located in "Mainmenu.map" that are used for the Main Menu. Vehicle bitmaps that are used in MP maps are located in Shared.map. Two weapon bitmaps are located in mainmenu.map: Plasma Rifle and Battle Rifle (because the Elite and MC models for profiles use these weapons). To determine where the bitmap you are skinning is located, use this picture:
If your bitmap is located and Shared.map or mainmenu.map, you must also upload those files to your xbox and clear your cache (Delete everything in your X, Y, and Z directories). WARNING: Deleting cache will result in a LONG load time for the first time you play after clearing cache, so just wait for it to load. You'll notice that Format is also circled in the picture. To determine what DXT type you must save it as, refer to that information. Here's what your save should look like (possibly more advanced depending on your dds plugin):
Where I circled, click there and select what DXT type you need. If it says DXT 2/3, select 3. If it says DXT 4/5, select 5. If it says DXT 1, select DXT 1 with 1 bit Alpha. Once saved, go to the proper bitmap tag and import it. Close the map and make sure you sign every map you modded, and then upload each map modified. Remember to clear your cache.
You may wonder if you can skin a vehicle/weapon for just one map. The answer to that is no if it does not loads from an external map such as mainmenu.map, shared.map, or single_player_shared.map. (At this time atleast).
I believe that covers everything. We currently have a problem with the hog's tires and the ghost's bitmaps. They turn black when you get too far away. Some say it's mipmaps but no one has figured it out yet (not to my knowledge). I hope this helps everyone.
