I know what you're going through. I've had a similar career path over the last 2 years since leaving the field of psychology. Your situation seems to be an inevitability when an employee teaches himself and learns at a rate that outpaces his current job description.

It is a very difficult situation, I know. You have learned and excelled very quickly, so quickly that your pay rate could not have kept up. Your company sees your abilities and your knowledge and wants to make use of it. Resentment begins to build as you realize that you are being taken advantage of.

The way I see it (and I'm in a very similar situation currently), you should take this project on. It will be excellent ammunition against your company when review time comes and you demand the pay you deserve. And, in the meantime, I would use this project as a resume builder and begin looking for other opportunities. Sometimes when people grow as fast as you have, they outgrow their company.

If you do choose to take on this project, I would advise you to not write a single piece of code until you have compiled an acceptable list of objectives. Since they have not offered any, it seems you will have to pull it out of them.

Thanks for sharing you dilemma,
--Dave