You can try to approach the owners but if they do not have it listed with a realtor it will be difficult to purchase it as a short sale. Buying a home at sheriff's auction is also very tricky, you usually have to pay cash or put a hefty cash deposit down at the aucttion and be prepared to close within about two weeks, PLUS you do not know what you are getting, you will not have had the chance to see the inside of the house or to have the home inspected so you have no idea what condition the house is in. It's a very risky business. And as the previous answer indicates the opening bid will be the amount of the judgment, so if the house is 'upside down', the owners owe more than it is worth, you really don't want it at that price.
Your best bet, if you cannot get to the owners before the auction, is to wait for it to come back on the market as a Bank Owned property. However, that could take quite some time. Are there other homes you are interested in? If so, you should find a good realtor and work with them to find just the home you want at a price you can live with.