I'm also using Windows Vista Home Premium. I dont think the version of windows is the issue. It has to be your graphics card, maybe the processor of your computer. The Z line is a very detailed route. Alot of the routes are. Couple of questions....
Does this happen with only this route or other high graphic routes like the Q or N?
What graphics card does your computer have?
Are you using a desktop or laptop? (on my current laptop, top of the line, I have no issues but when I use my HP laptop with a 1.2ghz processor & NVIDIA graphics, it tends to lag.)
Hopefully, some of the admins or other members can add to this and help out.