You will definately need a Realtor to help you with this, the banks will not work with homeowners as far as the short sale is concerned.
However, you should be in contact with your bank ASAP. Get them what they want. Start out with a hardship letter explaining that you can't pay the loan back why. One page letter be concise and to the point, they don't have time to read a novel, and quite frankly don't care about the fluff, just the details.
Good luck, stay positive, and they will help you through this.
If done correctly the bank pays Realtor fees, closing costs etc.