Microsoft on Monday plans to show off pretty much <A HREF="http://news.zdnet.com/2100-3513_22-5681655.html?tag=nl.e589">the dream portable computer</A>--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.