Can you still buy a new PC with Windows XP or do all new computers come with Windows Vista already installed?

The general answer for the question is yes. It surely depends on where you buy the computer. Many big markets have already installed a Windows Vista version on their PCs as they sell them. But some of the smaller shops, especially those that build your personal PC individully for you often let you decide whether you want to have Windows Vista or XP or even other systems like Mac or Linux. There is also a chance for you buying a computer with no system at all so that you can decide what to install.