I had the opportunity recently to test Linux, the freeware operating system, as a standalone, bootable CD. The version I tried was SimplyMEPIS 7.0, a configuration of the Linux OS and many popular open source programs, with a good graphic user interface (GUI).
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So why, you ask, would anyone want to switch from Windows? First of all, the price is dirt cheap and updates are easily available. The apps are also mostly free, so the overall cost of running a machine is low. You can install it on an older computer that struggles under XP and simply balks at Vista. And you can have it on your network with other OS with no security issues.
In fact, it's probably as good as any MS or Apple OS, as long as you want to run the basic apps. It's only when you get into gaming that Linux becomes a problem.