Dunno why your getting stuttery playback.

I can play HD Video fine on my old lappie with 512GB Ram & a Pentium 4, 3.2 GH CPU.

Stating the obvious really but make sure nothing CPU intensive is running in the background, virus check, any kind of scanning software?

Media Player wise I'd go grab yourself a copy of videolan, just google it, it doesn't have the flashiest of interfaces but it plays more or less everything you chuck at it. So grab that & run your video through that, any better?

Mind you if you are watching your captured video though power director, which I presume uses a small preview window & your video is jerky even then, then I am stumped.

Maybe a conflicting codec, maybe lots of frames were dropped when you captured the video?

Only thing I could suggest is to run your video through virtualdub (mpeg) & to convert it down to another format, xvid, divx, wmv etc.
But getting into re-encoding can be a bit of a learning step, mind you if you want to get into video editing then it's one you should take.

Hope this helps a bit, have a look at VideoHelp.com - Forum, Guides, Tools and hardware lists which has tonys of guides on this, that & the other