This may be a waste of time considering the Backtrack repos will most likely change for the final release. Also there is no substitute for the awesomeness that is backtrack, but if you want to get a few of the tools in your Ubuntu machine this is one way to do it.
In a terminal:
sudo gedit /etc/apt/sources.list
Add this line to the end of the file:
deb http://repo.offensive-security.com/dist/bt4 binary
Then do a ‘sudo apt-get udpate’ to update your repos.