Out of curiosity, a few days ago I tried running Knoppix. This is a version of Linux - a unix style operating system for PCs. The clever thing about this particular version is that you don't actually need to install anything on your PC - just stick the CD in the drive, boot off it and away you go.
I really was rather taken with this operating system. It's very configurable and has a good graphical interface. I reckon that it's no harder to use than Windows and it could very easily mature into a very capable desktop PC system. There's even a plugin called Crossover Office which allows you to run MS Office on a linux machine.
Microsoft's next version of Windows, currently called "Longhorn" will reputedly feature all sorts of clever bells and whistles. The problem is that it's likely to include some fairly stringent digital rights management and security systems, which could stop me from choosing exactly what I wish to use my computer for. It's still a few years away and by then Linux might well provide a very attractive alternative...