fault root password in Debian is 'root'. After you've logged in, you should change the root password and configure /etc/apt/sources.list to point to a Debian mirror near you.
UNetbootin allows for the installation of various Linux/BSD distributions to a partition or USB drive, so it's no different from a standard install, only it doesn't need a CD. It can create a dual-boot install, or replace the existing OS entirely.