There are a lot of great resources for gears but the work is significant.
The work drive is the same as a rack (generically) with 20 degree straight teeth. And the driven gear can be a typical spur/pinion. However, two things to be aware of; 1) PTC's revolve or sweep cuts are planar rather than the shape a cutter wheel takes on. The two are -not- alike. and 2) There are serious variations in worm drives based on many factors. What is sufficient and acceptable in your application can make a very simple task much more complicated.
Here's a good place to start: http://www.qtcgears.com/Q420%20PDF%20Files/Tech.pdf