Prepare Bootable Flash from Linux
From within Unity simply use the "Startup Disk Creator" utility that comes with the standard installation of Ubuntu. Open the Unity dash launcher to access Startup Disk Creator.
Once Startup Disk Creator is launched, click the "other" option to locate and load your distribution ISO image file. On the bottom of the interface select your USB Flash device or thumb drive.
Now click "Make Startup Disk."
The USB flash drive will be formatted bootable and the ISO image copied to it, making it ready for insertion in another PC for doing your Ubuntu install.
Prepare Bootable Flash from Microsoft Windows
The procedure to install Ubuntu / Kubuntu / Mythbuntu / etc... from a USB flash drive involves a straightforward process. Standard USB 2 flash drives are good for normal live systems. Typically the speed is between 4 and 20 MB/s. Your USB drive must be Fat16, Fat32, or NTFS formatted.
The flash drive will be erased during the process. You need a copy of the Ubuntu installer CD image (.iso) so that you can put it on a memory stick. If you are creating the installer USB flash drive from a system running MS Windows you will need the Universal USB Installer from Pendrivelinux.com. (Universal-USB-Installer-1.9.5.9.exe)
Run the USB Installer program and under Step 1, choose the version of Ubuntu you have downloaded, and uncheck Download the ISO. Under Step 2, click Browse and select and open the .iso file you downloaded earlier. Under Step 3, select your memory stick from the list (make sure you choose the right one). Check the box next to the list to say that you want to format the drive.
Click Create to put the installer onto your memory stick. The whole process should only take a few minutes. All of the files on the memory stick will be erased.