This is something I have found useful over and over again. It allows you to have fully functioning operating system that can be taken anywhere and used on any PC that has USB booting capability.

Here is what you need to start:

USB Flash Drive aka Thumb drive with 2GBs or more
Ubuntu Install CD (Can be downloaded for free from Ubuntu’s Website. Legally)
A PC with USB boot capability

To install Ubuntu to the flash drive is pretty simple.

Plug in your flash drive
I insert the Ubuntu installation CD/DVD
Restart your PC
Go in to your BIOS settings and change your boot sequence to boot from the CD/DVD, save changes and exit.
It should boot into the Ubuntu setup. Now follow all the prompts till you get to the drive selection.
Your flash drive should show up along with the other drive/s. Select your flash drive and continue the installation.
Once it is complete, reboot your PC.
Now you will need to go back to your BIOS and change your boot sequence to boot from your USB drive.
If all is well then it should boot right in to Ubuntu.

This can come in handy in many situations. For example say you get a bad virus and now your computer won’t boot but you have important documents, pictures or whatever. All you have to do is plug in your flash drive, boot up your system and you now have access to your hard drive along with all your files.