1. Download the Windows 8 .iso file
2. Mount .iso file (I recommend WinCDEmu, http://wincdemu.sysprogs.org/, but feel free to use whatever you want).
3. Make sure you have a bootable USB drive that has nothing on it and at least 4GB of space
4. Open the file directory of the .iso and copy all the files to the USB (Highlight all the files and drag to USB or right click -> copy -> paste to USB).
5. Once finished copying you will now have Windows 8 on a USB drive that can be used to install on any computer.
To install:
1. Plug USB drive into USB port
2. Start up computer and boot from said USB drive
3. Follow on-screen instructions to happiness.
Hope it helps