The WBuffer sample shows how to use w-buffering.
Source: (SDK root)\Samples\Multimedia\D3dim\Src\WBuffer
Executable: (SDK root)\Samples\Multimedia\D3dim\Bin
Press F1 to see a list of the usual commands. In addition, you can change the buffering mechanism by pressing W (w-buffering, if supported), Z (z-buffering), or N (no buffering). Note the artifacts that appear when using z-buffering.
W-buffering is a depth-buffering alternative to z-buffering, and should be used in cases where z-buffering produces artifacts. W-buffering does a much better job of quantizing the depth buffer.