Why do you want to sell if you are renting the property? Are you collecting enough rental income to pay for the mortgage every month? If yes, then I advise to hold on for a while. The Obama administration announced that it would adjust the so-called Home Affordable Refinance Program, or HARP, to make it easier for borrowers to refinance their mortgages, regardless of how much their home values have dropped. Hopefully, in the near future you can refinance at a lower rate and keep your home. If you are still considering doing a Short Sale, you will have to qualify with your lender to sale. This means you have to show a hardship -- loss of income, medical reason, divorce, unemployed, divorce..
I hope this helps, Linda!