http://pegasus.isi.edu/wms/docs/3.1/walkthrough.php

If you look into chapter 2.2, you will read

"After untarring a folder named Pegasus-3.1-Debian-6-x86.vbox will be created that has the vmdk files for the VM. Load this VM using Virtual Box. Once you see the simple Linux desktop, move on to the next step."

There is a glaring gap between "unzip" and "wait for the desktop". I just tried to get the vmdk into my VirtualBox, and had the choice of (a) do I need to use the conversion manager, or (b) do I need to import it, or (c) do I need to add it, or (d) do I need to create a new VM. (d) turned out the proper course of action, though that is far from obvious. Additionally, some recommendations should be given, i.e. memory allocation for VM, and "use existing" when attaching disk, selecting a 32 bit Debian Linux, etc.

I realize that with each virtualization toolkit the steps will be different, and even different versions of VirtualBox behave differently. I may even have suggest to keep the above sentence vague, but I realize the folly of it now that I had to explain it to a potential new user. We should fix this with a better description of at least on a high level what actions are required. It is not obvious from the documentation.