I just compiled a new map using Gmax, called ancient_forest, but when I opened it in Sapien and ran radiosity, the whole place was white and untextured! I clearly remember adding textures to my map, but yet they did not show up!

When textures are missing from your map in Sapien, this usually means that your shaders need to be created or edited.

If Tool created the shaders for your textures, open up each shader in Guerilla, check the box next to "Simple Parameterization", change the material type to what you want (sand, stone, ect.) and set the base map as the shader's respective bitmap. Detail maps should be set to your desired detail maps in tags\levels\b30 and then change your primary and secondary map scale values to 25.

If Tool did not create your shaders, open Guerilla, go to "New" and create a new "shader_environment" and give it the all the settings I mentioned above. Create a new shader for each bitmap and save your shaders in your tags root directory named after their respective bitmaps.

Once the shaders have "Simple Parameterization", a material type, the base map and detail maps along with detail map scales, re-run radiosity. The textures should now appear.

What does 'Simple Paramterization' do? I use it for all mine, but what does it do?

I'm not too sure, but I think that "Simple Parameterization" helps with the lightmaps/radiosity process to make it look better.