Well, for the PC version you use HEK+ (from halomaps.com) to decompile the single player map tags. This lets you extract the models and textures then you use fire batch texture extracter (again from Halomaps) to convert the texture files into normal graphics files.
I tried this process on the H2 xbox disk but I can't view the directory structure. So if it's just a copy of the xbox H2 disk then you'll have the same problem.