How to Install Ubuntu 12.04 from USB Flash Drive Easiest Way
1) Download the ISO file of Ubuntu 12.04 from here.
2) Download Universal USB Installer
3) Launch Universal USB Installer, and Click Next
4) Select the Linux Distribution from the drop down menu : Ubuntu 12.04 Desktop
5) Click Browse and select the ISO file downloaded in step 1.
6) Select the USB flash drive letter from the drop down menu, and Click Create
7) Done! After it will finish the process, you can use the USB to boot and setup Ubuntu 12.04 from it.