Trackballs

I get significant carpal tunnel symptoms when I use a regular mouse heavily.  For this reason, I use a trackball.  Unfortunately, I find that there's a very thin selection of trackballs available compared to mice, and more to the point, the trackballs I find suck.  Their cursor positioning is erratic, so that using the mouse for fine control means either slowing down greatly (move the mouse to where I want, wait for visual confirmation that it really went there, then click) or enough mousing errors to keep my blood pressure significantly elevated.

I would be willing to pay a premium price (though not a completely insane one) for a trackball that actually gave smooth, reliable, consistent cursor positioning without sacrificing the standard convenience features of a mouse (i.e., two buttons and a wheel).  Does anyone know of such a thing?  Alternatively, is it possible that there's a (WinXP) software solution?