The answer is that he restarted the machine. At an appropriate point, he put a CD with Ubuntu Linux on it in the drive. That made the machine ask whether he wanted a partition created (i.e., to load Ubuntu into a separate area of the drive from Windows, permitting one to choose to boot into one operating system or the other). He clicked, "no", and told the machine to just copy Ubuntu over the entirety of the drive, effectively erasing Windows.
Re: Okay, I'm an idiot.
The answer is that he restarted the machine. At an appropriate point, he put a CD with Ubuntu Linux on it in the drive. That made the machine ask whether he wanted a partition created (i.e., to load Ubuntu into a separate area of the drive from Windows, permitting one to choose to boot into one operating system or the other). He clicked, "no", and told the machine to just copy Ubuntu over the entirety of the drive, effectively erasing Windows.