I use Cyberlink PowerDVD 7.0. Everytime I started it up, Vista would pop up an message saying that PowerDVD would not support Aero and therefore Aero features (transparency etc. ) would be DISABLED. I see screen flickering and then PowerDVD starts. As soon as I shutdown PowerDVD, I see screen flickering again and Aero is back!
Well, good news is that Cyberlink has an updated build (#2211) for PowerDVD that you can download for free & it resolves this issue.