Microsoft on Monday plans to show off pretty much the dream portable computer–a tiny tablet computer as thin as ten sheets of paper with a camera, a battery that lasts all day, and a price of about $800. The only problem is that it’s still several years from reality. Microsoft commissioned the 6-inch-screen prototype, but still doesn’t know exactly when it will be commercially feasible. It will probably come at least a year or two after the arrival of Longhorn, the new version of Windows set to ship at the end of next year.