I downloaded Windows 8 as an ISO image, and I'd like to install it on a computer that doesn't have an optical drive.
Is it possible to install Windows 8 from a USB drive? How would I do this?
The Windows 8 installer is very similar internally to the Windows 7 installer. All of the other methods mentioned in the previous Super User post on How to Install Windows 7 from a USB Drive should work perfectly with the Windows 8 installer.
I would recommend using the Windows 7 USB Download Tool, as it's a very easy process — you just select the ISO, choose the flash drive, and it automatically formats it, copies everything over, and configures the flash drive to be bootable. I used it to successfully copy the Windows 8 installer onto a flash drive, and the installation went flawlessly on multiple machines.
(Note that when using the Windows 7 USB Download Tool, your flash drive will be automatically reformatted, so make sure to back up any files you have saved on your flash drive before starting this process.)
Windows To Go is a feature in Windows 8 Enterprise that allows Windows 8 Enterprise to boot and run from mass storage devices such as USB flash drives.
Softpedia has a USB installer setup if you need one
Here are a few links you should check out
I believe its fairly detailed explanation on these links.