well, for a new student the best thing would be to find a good teacher (that approves of you practicing on a low end digital), but since we all know that is unlikely, maybe buy a theory book to help you to learn to read and understand music, and a book of chords in diagrams to help you start playing right away, and a fake book of pop stuff so you can have some fun experimenting with what you learned from the theory and chord book.
Once you know how the piano works by reading the theory book, you are now open to do anything- maybe you are motivated to buy a better instrument, or listen to classical music and track down the sheetmusic for your favorites. What you do from here is completely up to you! Of course, the best choice is to get a decent piano and a competent teacher..
donjuan