This is a great question that many ask. Because you have a ratified deal contingent upon the third party you are not free to place a contract on another property during this time unless you are planning to purchase both. Depending on how your Realtor wrote the contract, you may be able to get out of the current contract and write on the new home if that is your goal.
This is the great frustration with short sales. Because they take sooooo long many times to hear back many people get tired of waiting and begin looking at other homes. Good luck.
At the outset, we tell the listing agents that we recognize the length of time it will take to get a response, and that we reserve the right to keep looking. The listing agent conveys this message to the negotiator in the hopes that they will expedite the process.
But if you are serious about another property more than you are about the previous offer you made, you may want to issue a withdrawal.