Here's how I got a few Aegir 2 VM running with Drush Vagrant. You'll need specific branches of some drush extensions (see below).
This is with my regular user. Do not use the root user for this (though it will if you opt to make it update /etc/hosts).
0) Check that you can do 64-bit virtualization. The basebox is 64bits.
1) Install through aptitude:
(Tested versions will be updated as I create new Aegir2 VMs.)
sudo apt-get install virtualbox vagrant
Note: At the time of publishing this article, the versions may have changed. All you need to do is have compatible versions, and vagrant will tell you if you don't.
2) Installed through php-pear:
# Install php-pear if not already present
sudo apt-get install php-pear
sudo pear install drush/drush
3) Go to ~/.drush, download git versions from drupal.org:
-aegir-up : branch 7.x-2.x
-puppet-drush : branch master
-drush-hosts : master
-drush-vagrant : 7.x-2.x
git clone --branch 7.x-2.x http://git.drupal.org/project/drush-vagrant.git
git clone --branch 7.x-2.x http://git.drupal.org/project/aegir-up.git
git clone --branch master http://git.drupal.org/project/drush-hosts.git
git clone --branch master http://git.drupal.org/project/puppet-drush.git
4) run "drush vb" (without the quotes)
-Enter the name of the VM
-Select option 6 (Aegir 2 dev)
-Press yes and wait