   What is filtering?
  Is filtering used for both 2d and 3d?  Is it just 1 call from DirectX or a huge chunk of code?   
  From Wikipediahttp://en.wikipedia.org/wiki/Bilinear_filteringhttp://en.wikipedia.org/wiki/Trilinear_filteringSo it will apply any time the texture is shrunk or enlarged, and since 2D is done through the 3D pipeline, it too gets filtered.  At one point in life 2Ds and 3Ds were seperate.  Now adays they are not.In open GL it's just a flag when creating the texture, I would imagine that it is similar in D3D.  I'm not sure about anistropic filtering though, doesn't that require extensions?   