Well, there's no such thing as a hardware MPEG
decoder (at least, none that I'm aware of), nor would Media Center know how to use it. It does, however, care about the MPEG decoder software(s) that you have installed.
As for the stuttering problems: have you yet installed the latest
AMD dual-core optimizer for XP? If you haven't, please do so - your stuttering issues should magically disappear.
And, yes, this is a legit deal, straight from AMD (they have issues with core-core timing under XP, under certain circumstances. MPEG playback in MC is one of those.)
~Chris
'nearly every day of my life is some kind of computer hell'
Desktop: Shuttle SN41 (AthlonXP 2700+), AIW, T550, PVR-USB2, HDHR; server: Intel E6400 on I965P mobo, 2GB RAM, 2x 500GB WD, PVR500, NV DualTV, Saber2020, 2xHDHR; Xbox MCX, Xbox360