if we're talking the barest minimum, anyone with a Windows PC really, absolutely must have a program in each of the categories below.
Browser: More than anything else, we use our computers to surf the web. Windows comes with a perfectly good browser—Internet Explorer. You can see how it fared against major competitors, including Firefox and my browser of choice, Google Chrome, in PCWorld's recent
Antivirus: Connecting to the Internet without protection is like leaving the front door open when you’re on vacation, with a sign out front proclaiming “Expensive stuff inside. No one home.” A good antivirus program, working in the background, provides the protection you need.
PDF reader: PDF files are all over the place, and everyone assumes—with good reason—that you have software that can read them. My choice:FoxIt Reader.
Beyond this bare-minimum list, there may be other categories to cover depending on what you want to do with your PC. You may or may not need a photo organizer, web-authoring tools, or an accounting program. You probably need an office suite, but I’m not going to say that’s an absolute, especially with so many web-based alternatives. There are programs, such as games, that you may not need but still want.