Most of the labs in the blog are using dynamips.

On each blog, a compressed lab file will be included. In the file you will find the following files:
  1. The .net file
  2. Initial config directory

If you are new to dynamip, the best place to start with dynamips is by visitin the Dynagen site.

After you have read the tutorial of dynagen, you can follow the screen cast I have created about using dynamips.