[1.7.10][LWJGL] Sub Viewport ? Custom sub window?

How can i render a sub window or glViewport?

public void Draw(int x, int y) {
	drawsScreen(x,y);
}

private void drawsScreen(int x, int y) {
	GL11.glViewport(x, y, 400, 400);		
	GL11.glLoadIdentity();
	GL11.glBegin(GL11.GL_QUADS);
	GL11.glColor3d(196, 196, 196);
	GL11.glVertex2d(x, y);
	GL11.glVertex2d(x + 100, y);
	GL11.glVertex2d(x + 100, y + 100);
	GL11.glVertex2d(x, y + 100);
	GL11.glEnd();
}