Here's the deal: Buy your dream home and pay only interest - no principal - for the next few years. That will give you an unusually low monthly payment while you get on your feet. Or better yet, pick one of our Option mortgages, and pay even less... . So goes the pitch for the hottest subset of the old-fashioned adjustable rate mortgage. With names like Interest-Only (I-O), OptionARM and Pick-a-Payment, these products offer borrowers far lower payments than they would face with traditional fixed- and adjustable-rate loans. According to some surveys, these especially risky products now account for half...