An easy way to install Windows 8 using a USB drive is by using a small program called Rufus
Steps to make a usb flash to be used to install Windows 8 using a tool
Rufus:
Insert usb stick into the computer operating system windows xp, vista or windows 7 and make sure if there's data, backup first. Download and run the program rufus (rufus_v1.2.0.exe) with administrator privileges (for windows vista and windows 7).
Select Usb flash, select the file system to be used (FAT 32/NTFS), switch mode Quick format, "Create a bootable disk using: MS-DOS" and "Create extended label and icon files".
Right click on the image icon beside a small drive option "Create a bootable disk using", then select the location where the ISO file is windows 8.
Next, click the "Start" button to start the transfer file2 of windows 8 iso file to a USB flash, and once the process is complete, the USB flash can be used to install windows 8 just like using a CD / DVD.
Keep in mind, once the USB flashdisk filled with windows 8 installation files, USB flashdisk can still be used as normal (just do not be formatted or deleted existing file2), whether it is used to store the data you (if there is space).
Note: Make sure the boot priority in the BIOS settings first using a USB stick.