First, how to delete the virtual machine (and in turn, Windows). So, the guides I linked you to describe two things. Subsequent to creating that virtual machine, you use a Windows disc to install an operating system on it - in this case - Windows XP. A virtual machine allocates some of your system resources and makes those resources 'pretend' to be another, standalone computer that runs in parallel with your native (physical) computer.
Parallels is a program that allows one to create what is known as a 'virtual machine'.
