How to make sure I can reinstall Windows 7 on DELL XPS 7100?

I bought this computer from DELL India online. It's not delivered yet. Just wanted to know that if I wanted to re-install Windows 7 Home Premium it comes with, what do I do? I don't think DELL supplies a Windows 7 disk. Many times computers get infected by viruses, and I want to make sure that I can re-install Windows 7 in such a case. Is there anything that I should do just after booting the computer up? Do I have to burn a DVD? If yes, how?