Help me with mu uni project PLEASE!!!

i've been asked to design and build a unit which will communicate via the computers parallel port, i've worked out the circuit and the software. But in the unit i need to have a 3 digit display in the form of 7-segment LED displays, these have to work as one, to display the data coming down the 8 lines in binary form, Can ne one tell me the logic involved, and if there are ne logic chips currently avablable.