Well maybe its all of those issues plaus other, maybe one or another issue has be the cause on different PC's
Right now I I use VMCD to change my default Decoder back to the RC2 decoder, I'll get the stutter and as soon as I return back to the Nvidia Decoder, it goes away, so I'm assuming we've found multiple issues that cause the stutter and your issue is just one that hasn't been completely discovered yet.
Give some of our know results a second try, it took me a couple time to get it working properly but once it did and I went back to be sure that was the cause each time I went back to the RC2 decoder, I get the stuttering again.
Hope you find your solution soon, it was very annoying for all of us I'm sure
System Specs:
Pentium 4 Processor 3.06GHz
2 GB RAM
GForce 8500 GT 512Mb
Hauppauge WinTV-HVR-1800
Creative X-Fi XtremeGamer
42 inch Samsung Series 5 HDMI
Windows 7 System Rating 4.0