Help me implement bloom effect

[babebabe]

I have and idea to implement some post effect like bloom, blur...
Standard instruction of this kind is:
  - Render this scene
  - Render/capture this scene to texture
  - Draw back this texture with effect to window clip with specify shader.
I done two first steps, when implement last step, I don't understand how CS shader system work  (I'm very new to CS), how I can draw one texture with specific shader (in this example is cg shader), and done by code, not by define in world scene. And this shader is only access to one texture and render target.
Thanks for advance.