Render Zbuffer to depth texture

[rockvider]

Hi,
i want to render the zbuffer to a depth texture, ive successfuly displayed the content of the backbuffer but i still have problems with the zbuffer this is my code:

// this is the intialization code of the textures	
zbuffer=new Texture( dev,dev.Viewport.Width,dev.Viewport.Height,1,Usage.DepthStencil,dev.DepthStencilSurface.Description.Format,Pool.Default );           
bbuffer=new Texture(dev,dev.Viewport.Width,dev.Viewport.Height,1,Usage.RenderTarget,dev.GetRenderTarget(0).Description.Format,Pool.Default);
// this is my rendering code
// i draw a mesh while im setting the render target and the zbuffer to the 2 textures i created 
//the bbuffer texture correctly display the mesh but the zbuffer doesnt display any data im using d16 depth format for the zbuffer
device.BeginScene();			
Surface oldbb=device.GetRenderTarget(0);			
Surface oldsb=device.DepthStencilSurface;			
Viewport ov=device.Viewport;			
device.SetRenderTarget(0,bbuffer.GetSurfaceLevel(0));
device.DepthStencilSurface=zbuffer.GetSurfaceLevel(0);			
device.Clear( ClearFlags.Target |ClearFlags.ZBuffer, System.Drawing.Color.Red, 1.0f, 0);			
SetupMatrices();            
for( int i=0; i<meshMaterials.Length; i++ )            
{                
// Set the material and texture for this subset                
device.Material = meshMaterials[i];                
device.SetTexture(0, meshTextures[i]);                
// Draw the mesh subset               
mesh.DrawSubset(i);            
}			
//restore the original render target and z buffer			
device.SetRenderTarget(0,oldbb);			
device.DepthStencilSurface=oldsb;			
device.Viewport=ov;						
device.Clear( ClearFlags.Target |ClearFlags.ZBuffer, System.Drawing.Color.Red, 1.0f, 0);			
//sp is a spirit used to display the zbuffer texture			
sp.Begin();			
// this one is not working just a white spirit appears			
sp.Draw(zbuffer,new Rectangle(0,0,device.Viewport.Width,device.Viewport.Height),new Vector2(0.5f,0.5f),new Vector2(0,0),0,new Vector2(1,1),Color.White);			
// this one is working and display the bbuffer			
//sp.Draw(bbuffer,new Rectangle(0,0,device.Viewport.Width,device.Viewport.Height),new Vector2(0.5f,0.5f),new Vector2(0,0),0,new Vector2(1,1),Color.White);			
sp.End();            
device.EndScene();            
device.Present();