What exactly is used for actually producing the wireframe models I'm not sure, although there is something called Mayo out there apparently which does a pretty good job.
Looking into it, there seem to be a number of programs all linked up such as wireframe production, shading, textures and scene fillers which fill in some of the gaps in movement.
The final stage is to render the scene which brings everything together into one big frame (ie: 1/24th of a second of animation). If you have Maya then you can buy Renderman for Maya which hooks the Maya animation system up with the Renderman rendering system as used by Pixar themselves.
Of course if you want to produce Cars or Toy Story, you'll need a render farm which requires a heck of a lot of computers, are quite a bit of time as apparently it takes 6 - 9 hours to render a frame with their system! But if you don't then it's probably possible to do it with a RAID 5 array I guess.
http://www.pixar.com/howwedoit/index.html
http://www.renderman.org/
http://en.wikipedia.org/wiki/PhotoRealistic_Re nderMan
Trev