Computer infection questions?

[Jondar]

I have tried downloads, on a variety of computers, which run everything from Windows 95, right up through XP. On every computer that I have ever tried, I have tried to stay on "safe" sites, such as Download.com, to download operations programs, screensavers, and so on (Download.com is just an example, of dozens of so-called web-sites I have tried). Wouldn't you know it, though. At evewry single site, that I can mention, I have brought back viruses, worms, and "tons" of spy-ware. And this is from the "clean", "safe", web-sites. I know that the best hackers can penetrate any connection, including D.S.L., dial-up, and any other connection, to inject bad codes into home computers. How can internet users "safely" use the internet, without having to worry about hackers, and corporations, "injecting" garbage into our computers? Any suggestions would be appreciated. unlock iphone 3g