Biome World Types Mod is desinged to make it possible to add a new world type for all or at least most of the biomes.
How to install:
Download and install Minecraft Forge .
Download the mod.
Go to %appdata%.
Go to .minecraft/mods folder.
Drag and drop the downloaded jar (zip) file into it.
If one does not exist you can create one.
Enjoy the mod.