FFDshow probably isn't needed for most DVDs if you have an 8 series card - I'm an ffdshut nut and even I gave it up when I got one.
If you're using Vista: try WMP with Dscaler. Seriously - WMP uses EVR, which (when it's happy with your drivers) gives an excellent, smooth image. Dscaler sucks as far as deinterlacing goes, but it's perfect for film DVDs which don't need that at all.
If you're on XP, WMP isn't quite so good. Try MPC in VMR9 mode with Dscaler, see if you can get it going without tearing. If so, all good. If not you'll need to get Zoomplayer or Theatertek - good time to get the latter atm btw, it's $40 (normally $70).
For HDDVD or Bluray, Powerdvd is the only real option at present. If you do get this, it contains all the video codecs you need for everything else, so don't bother with Theatertek also (a lot of the reason people buy Theatertek is for the purevideo codec it comes with). I've not tried to calibrate the new PDVD, but haven't noticed any colour problems - if it's smooth for you, you've got one app pretty much able to play everything.
Note this will be heresy to a lot of people, since PDVD has been fairly universally panned throughout its lifetime (and rightly so). However, recently they've got pretty much everything right (excepting still buggy HD playback!), and without the need for ffdshow it looks like a pretty good solution.