I read this thread along time ago and thought i posted to it but i guess not....
I'm on a DARPA grand challenge team at RIT and we got some software donated that might make this project a lot easier for you. It is from evolution robotics and basically it is high tech vision processing software. Now there are a lot of applications built into this software here are some i think you could use.
*planned and repeatable navigational tracks using virtual markers on walls and distinguishing points to give location
*Image memory. take a picture of a persons face for instance and then when it it is running if the web cam shows that person in real-time it will be able to identify them
*runs on a laptop 128 mb 433 <---cheap
*easy integration with many different sensors and interfaces
the software is a little high in cost but we got it donated just by asking in an e-mail. I think there is a demo version on their website. and even if you don’t use this software for this it is really fun to have your web cam identify you when you turn it on. Available in Linux and windows
http://www.evolution.com/
Hope this helps good luck with your project and let us know how it goes