Playing a retail DVD on Windows Vista Issues

i decided to go thru my dvd collection and found a movie i wanted to watch. i did not want to watch it on my tv, but on my pc instead. about 2 years ago when i used xp dvd playback worked, but not 5.1 surround. now, i can't get dvd playback on my vista. upon start of said dvd i get the following message:

Windows Media Player can not play this DVD because there is a problem with digital copy protection between your DVD drive, decoder, and video card. Try installing an updated driver for your video card.

now, i have an up-to-date video driver and i kinda remember something like this happening when vista first came out, but ignored it for i don't usually watch dvd's on my pc. i have klcp 4.0 installed as well. is there something i need to enable within klcp? are there some other appz i need to install?

what needs to be done in order for me to view dvd's on my pc? also, if i'm able to get playback how to get 5.1 surround as well? i'm unaware on how to view what codec the movie is encoded. i'm off for work or i'd be able to get some research done. hardware specs are in my profile if needed. help is appreciated. thx.