I agree with the previous answer - owner cooperation would be needed to buy pre-foreclosure.
The next point where there is a buy opportunity is at the sheriff sale. To buy there, a buyer needs a big pile of cash and needs to be aware of the "lien situation" of the property.
Your post assumed that the property would just become REO - but in the county where I track sheriff sales there are between 5% and 15% of foreclosed properties that are purchased by other than the bank at the sheriff sale. So it is certainly possible for this to never become REO.
There are already other threads posted on going about buying a specific REO, so I suggest searching a bit - this is a popular question and the answers have already been offered.