For this guide you won't need to download anything as all the tools necessary are already built in to windows. Specifically the program we will be using is called diskpart and it is already a part of your Windows installation if you're using 2003, Vista, 7 or above. I believe Windows XP also features it but I can't verify that as I do not have an XP system.
So to begin with, put your USB key in your computer and either mount the ISO of the OS you want to install (I recommend using SlySoft's Virtual Clone as it's free and works fine: http://www.slysoft.com/en/virtual-clonedrive.html) If you are going to be using a CD/DVD to create your USB stick then you won't need to download the above program. That is only if you have an iso file.
Now open a command prompt (CMD.exe) and enter the following lines one by one:
DISKPART
LIST DISK
SELECT DISK 3 (Change the number from 3 to the number that your USB drive is listed as)
CLEAN
CREATE PARTITION PRIMARY
SELECT PARTITION 1
ACTIVE
FORMAT FS=FAT32 QUICK
ASSIGN
EXIT
Now your USB stick has been setup all you need to do is copy the contents from your CD/DVD or ISO file (That you mounted earlier). To do that you type the following:
XCOPY E:\*.* /S /E /F G:\
(this assumes that your CD/DVD/ISO Mounted drive is E:\ and that your USB drive is G:\ - You should change these to your actual USB Drive and CD/DVD/Mounted ISO's drive letters)
After the copying is done you can take your USB stick from your computer and use it to install the operating system on other computers.
