First you need to ensure that VirtualBox is installed. Current vagrant release is not working with VirtualBox 4.x, so get a previous 3.2.x version (currently 3.2.10 which updates to 3.2.12) from http://www.virtualbox.org/wiki/Download_Old_Builds_3_2.
Next install the vagrant gem and download the Ubuntu 10.10 32-bit vagrant box I built up:
gem install vagrant
vagrant box add maverick32 http://dl.dropbox.com/u/2297268/maverick32.box