I ran PowerDVD 9 on my Dell Latitude D630, which has Core2Duo T7250, 4 GB DDR2, and Nvdia NVS 135M, running Vista x64. I was surprised how bad the quality was with Blu-ray playback. There was a significant amount of frame loss. I used to think the laptop as being able to do some heavy lifting, but apparently not so, at least for Blu-ray decoding. I'd guess the bottleneck is with the graphics core (rated at 3.8 by WEI, lowest among all), which isn't designed for this kind of task.
UPDATE: Same software works fine on a Dell Optiplex 760 with Core2Duo E7300, 2 GB DDR2, Radeon HD 3450, and Vista x86. GPU score is 4.3. CPU might be a factor too, now I think. The WEI on this machine is 5.5, while on the Latitude is a meager 4.9.