Take one stereovision camera (or build it with two identical IEEE1394 compatible webcam , you will get the requisite software from Carneige Mellon University repository) and apply SLAM (Simultaneous Localization and Mapping) technique. You will find out plenty of research material on the internet. Australian Centre of Field Robotics, are doing research in this area. Using SLAM adapt some behavior based robot navigation methodology ......I think this is enough (easiest way) for making a robot autonomous.

If you like I can give you plenty of research papers on this, because my area of doctoral research is also autonomous walking robot. At Chiba University, Japan, I am working on six legged robot (for land mine detection and removal) COMET-III. Presently we are working on development of fully autonomous walking robot (new one, under fabrication) COMET-IV. I am the key person having responsibility of developing it's brain (by artificial intelligence) and vision (stereovision based SLAM, also by AI principles). I have designed it's computer and instrumentation architecture.