LinuxBSDos.com posted a tutorial about installing Ubuntu 11.10 on external hard drive, with an ntfs partition at the end

How to install Ubuntu 11.04 on external hard disk, showed how to install Ubuntu 11.04 on a portable USB hard drive. This tutorial, written for Ubuntu 11.10, takes it a step further by showing how to add an NTFS partition at the end of an external drive – after installing Ubuntu.

It is a very simple process, but if you a new to this, and need some hand-holding doing it, this tutorial should be all you need.

To start, you need to, if you have not already done so, download an installation image of Ubuntu 11.10 from here. And of course, you need an external USB drive attached to the computer that you are going to use. So, burn the image you downloaded to a CD and boot the computer from it.

  Install Ubuntu 11.10 on external hard drive, with an ntfs partition at the end