Some code we use to ensure that we all use the same VirtualBox and vagrant versions.

vagrant_version_checks.rb

REQUIRED_VERSION = "0.7.2"
REQUIRED_VIRTUALBOX_VERSION = "4.0.2"

#Vagrant::Config.run do |config|
# ...
#end

# Ensure a compatible Vagrant and VirtualBox versions.
INSTALL_CMD = "gem uninstall vagrant -a -x &> /dev/null &&" +
              "gem install vagrant -v #{REQUIRED_VERSION} --no-ri --no-rdoc &>/dev/null"

unless Vagrant::VERSION == REQUIRED_VERSION
  print "You must have vagrant #{REQUIRED_VERSION} installed. Do you want to download and install it? [Y/n]: "; STDOUT.flush
  r = STDIN.gets
  if r == "\n" || r == "Y\n"
    puts "Installing..."
    status = system(INSTALL_CMD)
    if status
      puts "Vagrant #{REQUIRED_VERSION} installed successfully."
    else
      puts "Install failed? Try manually: #{INSTALL_CMD}"
    end
  else
    puts "Ok. Not installing."
  end

  exit 1
end

virtualbox_version = `VirtualBox -h|grep "VirtualBox Manager"|awk '{ print $5 }'`.chomp
if virtualbox_version != REQUIRED_VIRTUALBOX_VERSION
  puts "You must have VirtualBox #{REQUIRED_VIRTUALBOX_VERSION} installed (detected: #{virtualbox_version})."
  exit 1
end