just copy and paste this into your load method:

ModLoader.addBiome(Test); //registers the biome

After that paste this in the public static final area, we are now calling that the "Variables Section"

BiomeGenTest Test = new BiomeGenTest(23); //creates the biome

then create a new class called BiomeGenTest.class and paste this code:

package net.minecraft.src;

public class BiomeGenTest extends BiomeGenBase
{
protected BiomeGenTest(int par1)
{
super(par1);
this.theBiomeDecorator.treesPerChunk = -999; //-999 is equal to 0
this.theBiomeDecorator.flowersPerChunk = 4; //flowers per chunk
this.theBiomeDecorator.grassPerChunk = 10; //grass per chunk
this.fillerBlock=(byte)Block.glass.blockID; //sets the block that spawns below the top block
this.topBlock=(byte)Block.dirt.blockID; //sets the block that spawns on top
this.biomeName="Test Biome"; //sets the ingame name when f3 pressed
}
}

That's all of the code needed!