I'm assuming you meant "10.3.9", as in Panther. No, you cannot just switch users and install a new OS for that user. And you cannot install it onto a hard drive that you are going to partition. Well, you can but it would be a waste of time because partitioning a drive (the normal way) requires that drive to be completely erased. Kind of not worth it just for Popcorn. Or maybe you meant that you plan to partition, then install the OS. In either case, I'm guessing you just want to squeeze some ripped DVDs onto a single layer DVDR. No need to make a big to-do of it. Try this instead...
http://www.dvd2one.com/