I had a similar problem running Fullscreen HD on my Laptop
Problem turned out to be Vista, it has a process that controls all sound for Windows called Audiodg.exe.
This process is well known to cause both sound and video framerate loss on Vista as it sometimes tops out at more than 25% CPU Usage, for doing absolutely nothing.
I solved this the good old fashioned way, Upgraded to Win 7
You should have NO issues running on Linux, but give MythTV a try, now that's what HTPC Dreams are made of
GT220 even the GT210 will play 1080 no problem, just use "Media Player Classic Home Cinema"
http://mpc-hc.sourceforge.net/
No stuttering.
Guru3D have an article about it (page 9 of their review):
http://www.guru3d.com/article/inno3d-geforce-gt-210-and-220-review/9