I found this guide which describes how to create a dual-boot Windows 7 / Ubuntu system.
Is it possible to install Ubuntu as a "Virtual PC" inside Windows 7 (i.e. without using VMware or VirtualBox)?
It is not possible right now. VMWare or Virtualbox provide the outer shell of a system to allow such things to work. Windows does not have the tools to run an operating system within it. The only way to use Linux within Windows is to use Virtual PC, VMware, VirtualBox, or any such program of that nature.