Sure and although there are very few "preforclosure" properties where the owner actually has equity, you may be able to find the rare one. There will be other investors knocking on the owner's door so you will definitely have to compete with these sharks.
On a Short Sale then no the lender taking the often significant loss will require hte property to be listed for sale by a Realtor on the MLS system.
If you have all cash you can learn the ropes at the courthouse and buy at the auction. It's not for the risk averse and rookie, there are a lot of ins and outs. You may be able to hire someone to teach you the process. I think there are companies that will do that for a few thousand.
All the best,