If yo'uve been going to the andengineexamples google code repository and finding all the .jar files missing
If you look at his update:
"Now using related projects as Android library projects." It shows that you need to make a project containing the AndEngine source code which you'll update with Mercurial or whatever you use to update online repositories and then link your project to that project.
So pull a copy of the new repository and get back to your games!!
Tutorial:
1. Get the Source Code from GoogleCode and create a new Project with it
- If you're using Eclipse, use the Mercurial plug-in (Help → Software Updates in Eclipse, then install: http://cbes.javaforge.com/update).
- Go to File->Import->Mercurial->Clone Existing Mercurial Repository
- In the Repository Location URL box type in: https://code.google.com/p/andengine/
- Hit next. It should start cloning the repository...
- Then select the 'default' branch and hit next. Then ensure you have the box selected to import the project to your workspace.
And you're done importing the project! Now let's link your project to it..
This is what it should look like when you have them all imported:

2. Link your project to the project you just made
- Right-Click your project then Build Path->Configure Build Path...

- Then under the 'Source' tab hit "Link Source".. and select the src folder of the AndEngine project

Link this


And you're done!!

This can also be done with all the extensions! just go to the extensions forum and check out Nicholas's sticky link to the source code
Hope this helps guys! =D
