LaCie d2 & Power DVD BD 7.3

[SPUD]

Hello all,
Looking for some advice.
I have a LaCie d2 drive (shows up in device mgr. as "Matshita BD-MLT S-5582 USB device")
The drive came with Roxio Media creator 8.2 and PowerDVD BD 7.2 which I upgraded to 7.3 free of charge on line.
The PC spec:
P4 3.4GHz with hyper threading
1 Gig dual channel RAM
Radeon X1600 PCI express
Win XP pro

Problem:
Playback is stuttering (skipping frames) and the CPU usage is at or close to 100%. Hardware acceleration is switched on in PowerDVD. All drivers are latest versions.
I have only one BD disk at the moment, Casino Royale. All the intro video clips and animated logos play fine with low CPU usage 20 to 30% but once the main movie starts the stuttering starts. I suspect that the hardware acceleration is not taking effect because when I switch it off there is no further reduction in quality. About a month ago I temporarily installed a HD-DVD drive belonging to a friend on the same PC with PowerDVD HD 7.1 and everything worked perfectly. I can't remember what the CPU usage was with acceleration off but with acceleration on the CPU usage was about 50% and the movie played perfectly "King Kong".
Any useful advice would be much appreciated.

Jim.