The class that creates the FBO and the custom Renderer.

RenderOpenGL.java

package kamikaze.opengl;
import static org.lwjgl.opengl.GL11.*;

import net.minecraft.block.Block;
import net.minecraft.client.Minecraft;
import net.minecraft.client.renderer.OpenGlHelper;
import net.minecraft.client.renderer.Tessellator;
import net.minecraft.client.renderer.tileentity.TileEntitySpecialRenderer;
import net.minecraft.tileentity.TileEntity;
import net.minecraft.util.MathHelper;
import net.minecraft.world.World;

public class RendererOpenGL extends TileEntitySpecialRenderer
{

	@Override
	public void renderTileEntityAt(TileEntity tileentity, double x, double y, double z, float f)
	{

		glPushMatrix();
		glTranslatef((float) x, (float) y, (float) z);

		TileEntityOpenGL tileEnt = (TileEntityOpenGL) tileentity;

		if (!tileEnt.renderScreen.initialized)
		{
		tileEnt.renderScreen.init();
		System.out.println("init");
		}

		tileEnt.renderScreen.render();

		renderBlock(tileEnt, tileEnt.worldObj, tileEnt.xCoord, tileEnt.yCoord, tileEnt.zCoord, OpenGL.openglBlock);

		glPopMatrix();

	}

	public void renderBlock(TileEntityOpenGL tileentity, World world, int x, int y, int z, Block block)
	{

		//glTranslatef((float) x,(float) y,(float) z);

		Tessellator tessellator = Tessellator.instance;

		float light = world.getBlockLightValue(x, y, z);
		int l = world.getLightBrightnessForSkyBlocks(x, y, z, 0);
		int l1 = l % 65536;
		int l2 = l / 65536;
		//tessellator.setColorOpaque_F(light, light, light);
		//OpenGlHelper.setLightmapTextureCoords(OpenGlHelper.lightmapTexUnit, (float)l1, (float)l2);

		int dir = world.getBlockMetadata(x, y, z);

		glPushMatrix();
		glTranslatef(0.5f, 0, 0.5f);
		glRotatef(dir * (-90F), 0f, 1f, 0f);
		glTranslatef(-0.5f, 0, -0.5f);
		glEnable(GL_TEXTURE_2D);
		glDisable(GL_LIGHTING);
		glBindTexture(GL_TEXTURE_2D, tileentity.renderScreen.texID);
		//glBindTexture(GL_TEXTURE_2D, 10);
		//System.out.println(tileentity.renderScreen.texID);
		glColor3f(1f, 1f, 1f);

		glBegin(GL_QUADS);
		glVertex3f(1f, 0f, 0f);
		glVertex3f(0f, 0f, 0f);
		glVertex3f(0f, 1f, 0f);
		glVertex3f(1f, 1f, 0f);
		glEnd();

		//glDisable(GL_TEXTURE_2D);

		glPopMatrix();
	
	}

}

RenderScreen.java

package kamikaze.opengl;

import static org.lwjgl.opengl.EXTFramebufferObject.*;
import static org.lwjgl.opengl.GL11.*;
import static org.lwjgl.opengl.GL14.*;

import java.nio.ByteBuffer;

import org.lwjgl.opengl.Display;
import org.lwjgl.opengl.GLContext;
import org.lwjgl.util.glu.GLU;

public class RenderScreen
{

	public int fboID;
	public int texID;
	public int renderBufferID;
	public int width, height;

	public boolean initialized = false;

	public RenderScreen(int width, int height)
	{

		this.width = width;
		this.height = height;
	
	}

	public void init()
	{

		if (!GLContext.getCapabilities().GL_EXT_framebuffer_object)
		{
		System.out.println("FBO is not supported");
		//return;
		}
	
		this.fboID = glGenFramebuffersEXT();
		this.texID = glGenTextures();
		this.renderBufferID = glGenRenderbuffersEXT();

		glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, fboID); //Binds the fbo

		//Texture
		glBindTexture(GL_TEXTURE_2D, this.texID);
		glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
		glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA8, this.width, this.height, 0, GL_RGBA, GL_INT, (ByteBuffer) null);
		glFramebufferTexture2DEXT(GL_FRAMEBUFFER_EXT, GL_COLOR_ATTACHMENT0_EXT, GL_TEXTURE_2D, this.texID, 0);

		//RenderBuffer
		glBindRenderbufferEXT(GL_RENDERBUFFER_EXT, this.renderBufferID);
		glRenderbufferStorageEXT(GL_RENDERBUFFER_EXT, GL_DEPTH_COMPONENT24, this.width, this.height);
		glFramebufferRenderbufferEXT(GL_FRAMEBUFFER_EXT, GL_DEPTH_ATTACHMENT_EXT, GL_RENDERBUFFER_EXT,
		this.renderBufferID);

		glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, 0);

		this.initialized = true;

	}

	public void render()
	{
		glPushMatrix();
		glViewport(0, 0, this.width, this.height); //Texture width & height

		glBindTexture(GL_TEXTURE_2D, 0);
		glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, this.fboID);

		glClearColor((float) (Math.sin(System.currentTimeMillis() / 100) + 1) / 2,
			(float) (Math.cos(System.currentTimeMillis() / 100) + 1) / 2, (float)
			(Math.sin(System.currentTimeMillis() / 500) + 1) / 2, 1f);
		glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

		glMatrixMode(GL_MODELVIEW);
		//glLoadIdentity();


		glColor4f(1f, 1f, 0, 0f);
		glBegin(GL_QUADS);
		glVertex3f(0.8f, 0.2f, 1f);
		glVertex3f(0.2f, 0.2f, 1f);
		glVertex3f(0.2f, 0.8f, 1f);
		glVertex3f(0.8f, 0.8f, 1f);
		glEnd();


		glRotatef(180, 0, 1f, 0);
		//glFlush();

		glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, 0);

		glViewport(0, 0, Display.getWidth(), Display.getHeight());

		glPopMatrix();

	}

}