Spunk, the plug-in will be C++. There is a board here on the forum dedicated to plug-ins and videos in the support tab at the top of this page, video tutorials. Some docs too that will help.
Daniel, I think your right to an extent. I think it could be done but you wouldn't be able to trace very fast. Read, compare, adjust (jog a bit), over and over. Speed and resolution would effect accuracy.
Remember, these are just ideas and may not be pratical at all in the end. It may be better to use something like Tom's plug-in and then generate a path from that? Maybe you could scan what it is your trying to trace and draw over it and path it useinag a cad/cam package? I wish you luck and hope you can pull it off. If your new to plug-ins and C++ I think this would deffinatley be jumping off in the deep end but I'm sure if it can be done and you want to bad enough, you can do it. I think all things are possible but that doesn't mean their practical.
Brett