You could use smart chips so that you wouldnt need the robot to look for a barcode on the wall, lots of places use smart chips now they work some way i dont know, do some research.
You could use a vision recognition system like the CMU Cam
http://www.acroname.com/robotics/par...MUCAM-KIT.html
Also you could use a robot controller that is a single board computer, like the Via mini ITX robotics system
http://robots.net/article/983.html
Then you can have it access files stored on a hard drive and it would solve some of the issues you are having, maybe even just using an Mp3 player with your system in general. There are lots of websites about people building thier own Mp3 players im sure you can find somehing that will help you.