Screen captures of HD DVD movies is disabled in PowerDVD 6.5 or PowerDVD Ultra 7.2. Someone on the AVS forum has been successful with live captures:
http://www.avsforum.com/avs-vb/showthread.php?t=809002

You need this software:
http://www.irfanview.us/

The capture option will cap at what ever screen rez of display.

All captured at 1280x720 (screen rez) using Irfranview

EDIT: Using PDVD 6.5 with an ATI 9700pro
All are live screen caps and not paused/freeze frames