hi i am a totaly new user of ubuntu. i have recently built a new system and want to install ubuntu 13.04, i have downloaded onto an external usb hard drive from a windows system that is running XP. my question is this, if i turn on my new system that is running a blank hard drive but the external hard drive with ubuntu saved on it is plugged in will the computer recognise it and load it. i have used the normal download of the iso instead of opting to create a live usb, was this the right way to go. my next question is i know i can use ubuntu along side windows os but can i run ubuntu along side fedora linux with ubuntu as a dual operating system instead of windows as a dual OS system?
You need create a live usb from the Ubuntu.iso
You can install and boot as many OS as you wish limited by hard drive space, so, yes you can dual boot Ubuntu and Fedora.
I suggest you run both Ubuntu and Fedora live for a while and see which you prefer. Depending on your hardware, some people find the KDE versions faster then the gnome versions (see this weeks review on Distrowatch).