Don: I did a recent post called Arduino Lesson: How to Create a Library that may be helpful to you. I have not used the Web based IDE so I'm not sure what that is like. I would encourage you to go ahead and download the IDE software if that is a possibility. It's very easy.
TMCC is not on my resume but I think the idea is to send data through a serial port to the base unit over RS232. That should be fairly simple; see the Serial librarypage.
Great project! Good luck!
-- Leo