Assuming you are correct you should investigate short sales and then seek legal and/or tax advice in regards to whether this will work for you. A short sale in a nut shell is when the mortgagee (bank) agrees to allow you to sell the house for less than you owe. There are financial consequences to a short sale so ensure you seek proper counsel. It is an exasperating experience for all parties and I would most definitely find an agent in your area that is EXPERIENCED in working short sales. A lot of people choose short sales over foreclosure but you will have to determine if this will work for you.
Here are a few links for you to look at:
(this was front page on MSNBC today about short sales)
(definitely look at this website)
Lastly, have an agent visit with you about the what they believe the true value is on your home you might not be as bad off as you think (hope). And/or call your lender. You might be able to keep the home. A lot of lenders are willing to do what it takes to keep the house from going into default.
Best of luck,