New fully functional <A HREF="http://www.boston.com/business/technology/articles/2004/06/20/pluggedin_handtop_pcs_set_to_hit_mobile_market/">Windows-based handtop computers</A> will make their debut later this year. The new class of personal computing device is an attempt to pack in the hardware and software capabilities of a PC into a small rectangular box that can be slipped into a pocket.