Installing windows 7 via ext hdd HELP PLEASE!

So im trying to install windows 7 with an external, 500gb western digital hard drive. I am having like, THE worst time of my life because i just built myself an awesome gaming pc but i didn't buy a cd/dvd drive/burner. So if anyone could PLEASE help me that would be so nice and appreciated, please post before i rip my hair out :)

Hm. If you have another computer then this might work. Or, you could convince someone to lend you a dvd drive.