Thoughts about equity in a startup partnership?

My partner and I, we've went down the path of working together, built a product, and now begun selling it. We are now at a stage where we want to draft up the legal contract and wonder what other startups outline in their contracts.

We want to work on ramifications where if one partner looses interest in a project, the other may continue to pursue it; that is he would be penalized by reducing equity in the company. Also, what if one partners decides he wants to start working full time and earn an income, how does that effect equity.

Any thing we should be considering would be very helpful. Thanks!