You need one heck of a powerful CPU to view VC1/AVC encoded content, if your system gets no help from the GPU. That's the "Hardware acceleration" tick box in PowerDVD and WinDVD. If you can enable that, CPU utilization goes down by 40-50% or so. Depending on the GPU, of course. The problem is that not all versions of WinDVD and PDVD offer that option; some have it greyed out.
Please, feel free to call me by my first name, Petri.