I'm making another big push to get this problem solved as it has stubbornly defied all previous attempts. Right now I'm testing it with all tracking off to keep things simple. I've come up with some very strange results and I'm wondering not only if people can fix the problem, but also if they can replicate what I'm seeing. I've updated my drivers, but I still suspect this may somehow be an issue unique to my computer. You can download the world I'm running here (minus the music to keep the size down):
http://www.yousendit.com/download/T2...cTJ3TGg1VEE9PQ
Ignore for a moment that I'm a doofus and the 'w' and 'b' keys overlap the avatar head instead of replacing it. Althouh if people could let me in on how to fix that I'd appreciate it.
The main problem: Custom heads (including ones that come with Vizard) cause Vizard to become jumpy whenever the head is in the field of view.
Additional strangeness: I've discovered that if you are looking at the default avatar and then change the head to black and then change the head to black (resulting in a weird overlay) then suddenly things stop being jumpy, although they become jumpy again if you look away from the head and then back at the head. I have no idea what that means, but I'm hoping that it might suggest something to someone else.