How IT People Perfrom Reformats

I'm an IT Major at Boise State University and I often get a lot of people coming to me asking if I can reformat their PC for them. I was just wondering how most IT Professionals are able to reformat peoples PC's. Other then buying a new version of Microsoft Windows for every client, what service (if any) do IT professionals use? I know that Windows 7 Iso's are available online directly from microsoft, so theoretically if the person had their License sticker on their PC, you could reformat it using that. But as far as other software goes, (vista, office, XP, ect....) How do IT Pros do it? I've heard about Technet, but am not sure if thats what it's purpose is for.