This is a short guide on how to install Windows 7 onto a computer from a USB Flash Drive / USB Stick or Portable Hard Drive. Since read speeds are faster from USB drive than your CD-ROM drive, this actually decreases the install time for Windows 7.
How to install Windows 7 from a USB Drive
The first thing you will need to do is format your USB Flash Drive or Portable Hard Drive so that your computer will read it as a bootable drive. So plug your flash drive into a workstation.
Open up Command Prompt / CMD (located in Program Files->Accessories) and type the following commands:
List Disk (this will list the disks currently plugged into your computer. Most likely, the C: drive on that computer will be listed as disk 0, and you will have to look down the list to see which disk your flash drive is. Look at the corresponding disk sizes to easily figure it out.)
Select Disk 3 (I am using 3 as example for assigned flash drive)
Create Partition Primary
Select Partition 1
Format FS=NTFS Quick
Assign (you can assign a particular drive letter if you want, example: assign=E:)
Exit (this will exit DiskPart)
Exit (this will exit CMD)
Next you will need to either insert your Windows 7 CD and browse to the CD or open up your Windows 7 ISO and browse to the folders within it. (If you are using ISO, I would suggest extracting the contents to a new folder)
Next you will need to spoof your flash stick so that the computer will think it is an install CD. From within the root of the Windows 7 CD or ISO contents, right click while holding shift key and select “Open Command Windows Here”. This will open up a Command Prompt window within that directory. Then input the following commands:
bootsect /nt60 E: (I am using drive letter E: as my flash drive)
exit (exits command prompt)
Next simply copy over the entire contents of your windows 7 CD or ISO to your flash drive.
Reboot the computer your are wanting to install Windows 7 on with the flash drive plugged in, hit the boot key (normally F12, DEL, or ESC) to select the boot device, boot to your flash drive, and it will go immediately to the Windows 7 Setup screen.