Buring DVD's Windows Vista Video Scrambled

I have recently installed Windows Vista Business editon. Now when I when I burn DVD’s and then play them either by DVD player or on a Computer the video seems to be scrambled or very blocky. I have tried using Roxio 9, Nero 7, SwiftDisc, ImgBurn.

I didn’t have a problem in Win XP Pro SP2 with Roxio 9. Any Suggestions?

I am using a Plextor PX-716a firmware 1.10. Pentium D 805