NEW YORK (Money Magazine) - Lisa Boxer is suffering from sticker shock -- and not from the cost of a new car or refrigerator.

In May her husband was transferred from Florida to New York City. That gave the couple four months to find, buy and move into a house in a New York City suburb with suitable schools for their two kids. At first, Boxer simply couldn't believe the prices -- understandably, since prices in the New York City metro area have jumped 21 percent in the past 12 months.

Eventually, she shrugged and accepted the fact that they were going to have to spend more money for less house. Still, Boxer says, she's worried. Will paying such a high price lock her into this house forever?

In other words, is there a housing bubble? And if so, when is it likely to burst? Nationally, housing prices have risen 31 percent over the past five years, including 7.4 percent in the past year alone -- rates significantly higher than the historical averages. Yet Alan Greenspan, testifying before the House Financial Services Committee in mid-July, said it doesn't look like a bubble to him. And most economists seem to agree.

"The supply of homes is very lean by historical standards," says Lawrence Yun, senior economist at the National Association of Realtors. "We also have the lowest mortgage rates in 35 years." Yun adds that people are making larger down payments on their homes than in recent years, giving them more equity should they need to draw on it. Finally, consider the fact that, since the NAR began keeping records in 1968, home prices in the U.S. have never declined nationally from one year to the next, and you've got a pretty compelling argument.

But notice the word nationally. We have certainly had regional hiccups. Between 1989 and 1991, for example, New York City metro-area housing prices experienced an annualized decline of 3 percent. And, notes Celia Chen, senior economist at Economy.com, evidence suggests some regions could be headed for a fall right about now.

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Chen maintains an index of "house price equilibrium" in the 140 largest metropolitan areas. Her spreadsheets calculate whether current prices for single-family houses are fair, based on the demographics and income growth of the population, as well as on interest rates. The higher the index number, the less fundamental basis there is for the region's overall housing price increases. Of course, specific places within one of these large metro areas may be experiencing price increases for reasons of their own.

But, she cautions, high prices themselves don't necessarily indicate a bubble. For that, you also need excess supply. Factors that inhibit supply -- zoning laws that limit building, for example -- may prevent a bubble from forming. That's what keeps expensive places like Boston--or Westchester County, New York where Boxer is focusing her search -- off Chen's list of problem areas.

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Chen also points out that just because there's a bubble doesn't mean it will burst. "You could have a slowing, where house prices advance at the rate of inflation or not at all but wouldn't be a terrible hardship on most families," she notes.

How can you protect yourself in an environment like this? Be smart about the house you purchase. Look for good schools, a decent block, expansion potential and curb appeal. That's what Lisa Boxer is trying to do. "We're willing to compromise," she says. "We'll take a house that's too small, a commute that's not perfect or schools that aren't No. 1. We just don't want all of those things at one time."