You may be able to find out what aircraft is going to operate your DL
flight, but it may be a lot of work as well. First of all, find out what aircraft type (Boeing 737, MD
-88,...) is going to be used, then head over to http://airfleets.net
and see a list of all registrations within the DL
fleet. Then, enter one by one in the "Flight/Tail#" menu on top left of the site http://flightaware.com/
. Chances are you will find the N-number of the aircraft that is going to operate your flight, but only about one or two days in advance of it. And as flyingalex pointed out, these schedules are subject to change up to the last minute. I have made this experience myself...
'He resembled a pilot, which to a seaman is trustworthiness personified.' Joseph Conrad