Have you looked through the links Barrett mentioned above? What are your software development skills and/or interests? Do you have a hobby, side business, or other activity that might benefit from a bit of artificial intelligence? Do you have some complicated data (and lots of it, preferably) that you think could use some AI to make sense out of it? Do you want to do something with electronics (you'd have to be willing to spend money).
Your first step is to do some brainstorming. Projects come out best when the main person is passionate and committed to reaching an endpoint because it meets some highly desirable goal. Try googling terms like these:
how to brainstorm
brainstorming science fair projects
Brainstorming is in essence fairly easy. Get a notebook and pen and just start writing interesting phrases related to AI, and develop the ones you like best. "Develop" just means to write even more interesting phrases about the good ones. This will do two things, 1) help you find ideas, and 2) help you put ideas aside, which is just as important. Every few minutes copy the surviving ideas to another sheet of paper and keep going. If you can do this in the presence of one or a few trusted friends, you'll go even farther, faster.
Try going to freshmeat.net and searching for "artificial intelligence." That will give you some ideas and you'll be able to download some programs that have to do with AI. Playing with them will give you even more ideas. Another source of open source software is sf.net.
Let us know how it goes. Good luck!
Science Buddies Expert Forum