These instructions were tested on a virtual machine running a pristine new install of Ubuntu 6.10 (Edgy Eft). These instructions should work exactly as entered on such a machine, and to the degree that your machine varies from this pristine model I've used, so will the instructions.
Step one: enable universe repository
sudo gedit /etc/apt/sources.list
uncomment the two lines that add software from universe
deb http://us.archive.ubuntu.com/ubuntu/ edgy universe
deb-src http://us.archive.ubuntu.com/ubuntu/ edgy universe
Step two: Make sure you're up to date:
sudo apt-get update
sudo apt-get dist-upgrade
Step three: Install everything under the sun!
sudo apt-get install ruby libopenssl-ruby1.8 ruby1.8-dev rdoc irb
gunzip < rubygems-0.9.0.tgz | tar xvf rubygems-0.9.0.tgz
sudo ruby setup.rb
sudo gem install rails --include-dependencies
Step four: download Metasploit and unzip it
gunzip < framework-3.0-beta-3 | tar xvf -
Step five: Start up the application
open browser to http://localhost:55555
I hope this helps someone to get Metasploit 3.0 running on their linux machine. I hope that someone will then write a posting telling us how to do stuff with metasploit 3.0 because there are some new options and the old stuff doesn't work quite the same.