Help with USB Installer creation?

Ok so I want to dual boot my current Mac OSX (Lion 10.7.5) and Windows 7 Ultimate. I have an ISO for Windows, but I would like to create a USB Installer, rather than use a CD/DVD. Currently, my Boot Camp Assistant (v. 4.0.4) Does not give me an option to create a USB Installer. I'm not sure if that is because it doesn't recognize the USB (Which is in FAT Format) or because it's not able to create a USB Installer. Sorry if there was anything unclear. Feel free to ask questions! Thank you, in advance, for your help!