The only way I can see you moving is if you move to a new build and the builders do you a good part exchange deal (possible in this climate), but even doing that you're going to need a fairly big deposit. Sit tight, change your mortgage if you can get a cheaper rate and save up a bit more would be my advice.
....oh yeah, and if you are in negative equity, make sure your mortgage is repayment and not just interest only so you are chipping away at the loan all the time.