Getting involved in startup, equity negotation advice?

[durron597]

An acquaintance from High School (let's call him Joe, not his name) recently got in touch with me through a mutual friend about being involved in a website startup idea he has. He told me the idea, we've had a few meetings at this point, the idea is pretty fleshed out.

Background: I am a programmer, Joe has a finance background and background in the industry the site is in (I do not).

I told him that I am willing to do this in my spare time, working for equity. I am contributing $0 financially to this endeavor, only my time. He will pay for web hosting, servers, etc., and he will do all marketing work involved (which will be fairly substantial).

There is a third person involved who will be hosting the temporary server for development until Joe buys access to what will be our production server. He is also a programmer, with a significantly less "polished" background than me, but has more experience in our specific development environment. I am not sure what Joe has planned as far as this person's share of the equity.

So my question becomes: how equity much am I contributing? Obviously I want to figure out what the equity would be before I do anything; should I be setting up a contract with a lawyer now? When he approached me, he said "I have programmers, I am looking for a partner."

Thoughts?