I have the same problem with
PowerDVD 7.0 Trial version, but
I can close the process from systray. Often, the problem is in the same point of the DVD and it happens with different DVDs. I have the lastest drivers of all components and DirectX (9.0c).
The version is the lastest (downloaded on Agust 3 '06).
Intervideo
WinDVD 7 works perfectly.