from Sep 21, 2006 says to use NVidia PureVideo Decoder to decode (on the card's hardware) and then add FFDShow on top to sharpen and resize.
That was my biggest confusion - how to use PureVideo and FFDshow together.
EDIT: After spend hours trying to configure FFDshow + NVidia PureVideo + Media Player Classic + X-Fi Elite, I couldn't get them to work. Even more frustrating, the FFDshow audio configuration screwed up my X-Fi Elite Pro configuration. So I just uninstalled the whole FFDshow and MPC.
I have an NVidia 6800 Ultra but always used the control panel in the "classic mode." Since I read some more threads on here about the NVidia driver settings + PureVideo, I decided to switch to the new mode. Duh!!! The options to sharpen and noise-reduce are right there on the video->advanced tab! And they work in real-time. I played a couple of DVDs and slid the tabs back to forth to see the difference. Wow, they really do sharpen up the image. I bought the NV 6800U the very first week it came out a 2.5 years ago. And all this time I had no idea I could sharpen & denoise video!
I believe in K.I.S.S. If you don't have hours/days to mess around and possibly have to rebuild your PC, and want to use Windows Media Player or WinDVD, just use an NVidia card w/ PureVideo and the advanced settings.
I do wish, however, that someone could write an installer for FFDshow that would configure it automatically to work with PureVideo and MS Windows Media Player and/or WinDVD.