Training for Shake 2.5?

Hey everyone. I'm an Avid editor with a lot of After Effects experience, but am looking to get into compositing and visual effects. Most of the AE work I do is motion graphics, but I'm very familiar with using it for compositing as well. I have Steve Wrights book on compositing as well as Mark Christienson's AE compositing book. Since I want to get into compositing seriously, I thought I better get cracking on node-based applications.

I don't have a ton of extra money to spend, and so picking up Nuke or Toxic or any of the "newer" programs are kind of out of the question. I'm also a PC guy and don't have the money to spend on a Mac. Since I'm still in learning mode and don't want to spend too much money, I want to try to get my hands on Shake 2.5, which I believe was the last Windows version.

Anyway, with all that background info out of the way, here's the question. I was looking into getting Marco Paolini's Shake 4 book because I hear unanymous praise for it all the time, but was unsure of how different 2.5 is from 4. If I read through the version 4 book, could I follow along pretty easily using 2.5? I know in AE if I were to go back a few versions, there's a pretty significant difference. I'd still like to learn ver 4, that way I know it if I ever have to use it in a professional situation, but still would like to follow along using 2.5...would this be problematic for me?

Sorry for the long post and thanks for any help you can give.