An alternative method:From your question, I don't see any specific reason why you would want to put Debian onto a USB stick (if there's one, correct me). If you really just want to dual boot Debian on a machine running Windows 7, the Win32-Loader offers an easy way to do so. One can grab this from any debian mirror, inside the directory debian/tools. It's easy to use and self explaining. Once executed, just set the options to your needs (things like keyboard layout are automatically detected) and then click the install button. The setup will download the needed files and then allows you to directly boot into the installer, without the need for making an USB stick bootable and copying a lot of files on it.And yes, the Debian installer offers a way to partition the disk.