Step 1: Open a command prompt with administrator privileges by clicking on the Start button, then type cmd in the search box and press Ctrl+Shift+Enter.
Step 2: At the command prompt, type diskpart to enter the diskpart utility.
Step 3: At the DISKPART> prompt, type list disk.
Step 4: Type select disk 4, where "4" is the number of your USB flash drive from the list.
Step 5: Type clean to clean the USB flash drive.
Step 6: Type create partition primary.
Step 7: Type active, to make the partition active.
Step 8: Type format fs=fat32 quick to format the USB flash drive quickly in the FAT32 file system.
Step 9: Type assign to have Windows assign a drive letter to the drive. Type exit to leave diskpart and type exit again to close the command prompt.
(Credit: Screenshot by Ed Rhee)
Step 10: Insert your Windows 7 disc into your computer and copy all the files to the USB flash drive.
That's it. Once the Windows 7 files have completed copying, insert your USB flash drive into a computer and boot it up to start the Windows 7 installation. Just make sure that the BIOS is set to boot the USB flash drive first. On some computers, you can press an F key to set boot options.