Re: formating external drive with ubuntu so I can boot from external drive
If you want to keep the data on the drive, you had best back it up or copy it onto a different partition than the one you intend to use for your install. It is never a requirement to back up anything, ever!
The source for getting software is through the various distributions of Linux, there are many. What is best is something that each individual must determine for themselves. You are on Ubuntu forums here so that might insinuate that you are planning to use one of its variant distributions. After you make your choice you have to download a copy of it to your existing system and make a "live" disc of it, dependent on its size, it will fit on either a CD-R or a DVD-R. You must burn this .ISO file onto the media before you can install it on your system.
The remaining software, of your choosing, comes from centers of distribution that are set up all over the world, through what are known as repositories. It might sound difficult, but it is made very simple, though it is likely you will find a bit of learning curve dependent on your abilities with computing.
Best of luck
AMD 64 bit, 2 Gb ram, UbuntuStudio 14.04.1 (main system) and Xubuntu 14.04.1 /KXStudio repos (recording system).
Playing and recording, my music, my way.