The only people who can accurately tell you impact on your credit score is Fair Isaac, who created FICO scoring and keeps the formula quite secret. Per their consumer site (myfico.com) there is effectively no difference in how they score a short sale versus alternatives (see link). I would suspect you'll take a hit on your credit, though most of the damage is likely already done via the string of 120-180 day past due records on there already.
As to when you can buy again, it's anyone's guess. I will say you're in good company as there's no shortage of people facing situations just like yours. And there are still far too many homes in the U.S., as will be the case for the foreseeable future. I would suspect a couple years down the road when the housing market bleeding has slowed mortgages will be issued less by virtue of a three-digit credit score rank with a 7-10 year memory, and more by a credit score reflecting two year's past performance, your debt and income/job history/stability.
Given the housing implosion continues onward, I would doubt you'll be able to secure a mortgage from anyone other that government-backed mortgage (too much risk for private entities, who can't sell mortgages at market rates due to crazy forced lending from government-sponsored competition) -- and I don't believe Fannie/Freddie is an option for you at the moment with a recent short sale. Rent in the short term, kill as much debt as you can and stockpile down payment cash the next couple years. You'll most likely be in a good position to buy a house at prices significantly lower prices in a couple years.