I'd be in to do it as well, I NEED the experience in an open source project or any project in general, I've been programming c++ since I was in high school so I am very proficient in that regard, and I know basic Discrete Math and some Linear Algebra, and Introductory Computer Architecture. I've been working on my own Game Engine but I've put that on hold since I'd have to spend a lot of time diagramming and documenting what I've done, which I don't want to do if its not set in stone. if it helps, I know about basic gui design as I've worked with wrapping WINAPI before. I know what data structures are and when to use what type of data structure, for instance a queue for handling keypresses or window events.
Edit: If you were to allow me to join it can't be a full time thing, my part would have to be a bit asynchronous since I'm still working on School.
Double Edit: I WOULD LOVE TO WORK WITH SFML, it looks beautifully designed and I've been thinking about instead about using IT instead of designing over "pure" OpenGl and DirectX for the game engine that I'm working on. If I'm to join I hope that this is a serious project, because the last team I worked with had only 2 other programmers and the project leader didn't do much at all. I hope to learn a lot in the design regard, If its not already done :).
Triple Edit: If networking is not done, I'd be happy to lend a hand, Since I know that SFML has a completed socket library for simple TCP/IP/UDP sockets. I've made my own socket library before that was similiar but IMO better, that got deleted unfortunately :(. I am a jack of trades, master of none, but I'd prefer to work in the graphics sector of things and MASTER that niche area. Since you guys say its a 2d engine it should be relative easy to work with since SFML already handles rasterization of 2d images and simple stuff like timers.