AFTER struggling to fix up a brownstone in Harlem for the last 16 months, Meyghan Hill, a model and actress, and her husband, Daniel Scarola, a ballroom dancing instructor, are thinking about giving up and moving out. But what may drive them away is not the neighborhood, which they have come to love, nor their four-family house, where they have painstakingly stripped a century of varnish and paint from doors and balusters, but the shock of a tax notice they received last month from the New York City Department of Finance. The notice indicated that the taxes on their 19-foot-wide...