Ok, you're starting to get on my nerves.
You may be 13 but that gives you no excuse. This kind of attitude is that which gets people banned on forums.
The Arduino (spell it right) is a microcontroller running at 16MHz. One of my crappy desktop computers is 1.6GHz (1600MHz). You think you can get an arduino to do the same things as that old thing? No?
The Arduino also has about a 500-1000 times less RAM than most people's computers.
You cannot create any kind of decent OS for it, it's hard enough doing a simple scrolling menu on a VGA monitor, let alone rendering even an image of a windows desktop.
Grow up a little, scrub your mind of this stupid idea and come back and think a little before posting.
Mowcius