I thought I would share this as I always seem to have the need to install Operating Systems without a CD ROM drive.
-Insert 4 GB USB flash hard drive
Open Command Prompt and if using Windows Vista or 7, make sure you run as Administrator
in command prompt, type diskpart and then list disk (it will then list the available drives, make sure you select the correct one!)
-Now format the drive by typing the following:
select disk 1 (or which drive is correct, check size it helps)
create partition primary
select partition 1