Adding New Biomes
The mod comes with build-in support for Biomes'O'Plenty, Highlands, and ExtrabiomesXL. Adding any new Biomes or native ones I might have missed out just drop a picture in a TexturePack. To properly function you will need the Name of the Biome. You can get it by pressing F3 ingame. The names need to be lowercase and the spaces replaced by underscores.
An Example Pack on how it should look can be found HERE.