judging from the info on their website, Pure Motion Edit Studio 3 looks like a program that would be good for a beginner who wants something that will step him through the process but with some room for creativity.

VV3 is much more powerful and it's a blast to use. I showed my wife, brother in law, and 13 year old sister how to use it in minutes and they each have made their own movies that are very creative and expressive. one of Vegas's strongpoints is an interface that lets you focus on being creative instead of technical details.

I like the story-board style editing window that PMES3 has, and another interesting thing to note is that Pure Motion Edit Studio 3 comes with a Pixelan Spice Master - like transition filter called Herb Garden. this allows you to use grayscale images as a key for a transition to make some cool interesting wipes. we Vegas users have to buy Spice Master separately for that functionality, but the extra cost shows. VV3/Spice has an easier & more powerful interface.

feature wise and interface wise, VV3 makes Pure Motion look very basic. my recommendation... is to download the VV3 demo and see for yourself.