You may write an offer and present to the listing agent. Unfortuntely, if this is a foreclosure, the bank does not have to review the offer or accept it, if they already have one in process. Five minutes can make a difference.
You might want to keep in touch with the listing agent to make sure that the offer is proceding with no problems. If you have the time to wait, the house may be back on the market, if the prospective buyer does not get the loan or the bank does not like the terms.
In any case, the seller chooses whether or not to accept any offers on his/her home.