A constant 25-30% CPU load is actually a bit high and leads me to believe that the hardware accelaration is not working properly. However, if the CPU load is spiking or pulsing, then it's fine, as my PC does the same thing. You may want to playback some pre-recorded HD content and see what sort of CPU load you get. If it's in the 5-9% range, the hardware accelaration is indeed working properly.
If the CPU load is constant 25-30%, I'd suggest downloading the Cyberlink PowerDVD 8 trial version and using it's supplied H.264 and AAC codecs; instead of the MONOGRAM AAC codec, which I found to be rather poor. I think that one can still use the Cyberlink codecs even after the trial software expires.
If you don't wish to download the entire PowerDVD 8 trial - it's ~100 MB - then the H.264 codec from it can be found at the below URL: