However if you do need rental income to qualify, and since you are upside down, and if you are buying in the same area as your current primary residence, then you will need to claim the rental income on your tax returns and then it'll be considered a rental property and thus not need the 25-30% equity that loan programs need you to have in order to use rental income from a vacating primary residence. The longer you have the renter in there the easier time you'll have using the rental income, but there is no predefined amount of time other than having reported it on your most recent tax returns - so if you rent it out now and in early 2012 you'll have filed your 2011 tax returns with the reported rental income you should be good to use it as long as you still have a renter in there. There is also no 20% down requirement in order for that to be possible - you could purchase with FHA financing & 3.5% down or conventional financing with as little as 3% down (with 5% down you can avoid monthly mortgage insurance).
Shane has given you some great advice. The real question is one only you can really answer, how badly do you want to move? Assuming you are willing to live with mom & dad for a while and your motivation is high, I would suggest the sooner you get started the better. Time will eventually straighten out much of the market; we just don't know how much time.
With the current environment of low rates & prices and your good income, save some money, pay off as much debt as possible and get a tenant. If all goes optimally, you'll be able to buy while prices & rates remain low and the market will move up providing you improved value in both places. No guarantees, just my wish for you.