I guess I'm not sure what you're asking here. This is my take:
1. Your current property is "upside down" in value. You can either attempt a short sale, rent the place out and keep making your payments, let it go in to foreclosure.
2. If you have a mortgage payment that you're currently making on the house and you have a renter in there, it might allow you to get a new mortgage if you have enough for a downpayment. Thing is, in order for the lender to take that in to consideration, you will need to have rented it for at least 6 mos. to a year.
3. If you do a short sale or go in to foreclosure, you will not be able to purchase for a couple of years after the final execution of either.
I know this seems a little overwhelming. You may want to talk to a good agent there just to get some advice and lay your scenarios out in front of you. Couldn't hurt to consult an attorney either.