Walk through some of the region's newest neighborhoods and you'll discover hundreds upon hundreds of houses lying empty. Their owners, victims of foreclosure, have long since moved on. While only some of those are currently on the market, you'll find it next to impossible to come upon a foreclosed home for sale in Sacramento's central city. That's because there's currently only one. The desirability of living in the grid and of its housing stock have kept prices fairly stable and made the area nearly immune to the foreclosure crisis, unlike outlying areas of the city and fast-growing suburbs like Natomas and Elk Grove, according to local real estate agents. "Downtown has held its value,