Need help, building a vending machine, need it by

I have been tasked with building a vending machine by Sunday morning for the University of Chicago Scavenger Hunt. I have on hand a sparkfun serial lcd, arduino mega, a ps/2 keyboard, and a infared slot detector . I would like to interrupt the slot, have the arduino display a prompt and then take a three digit number from the keyboard, then depending on the number, it would switch a selected digital output. Would anyone be willing to throw together some code, or atleast point me in the relevant directions? I have the LCD working to the point I can print text to it, but I can't figure out how to use the LCD and keyboard together.