Since the possibility of disputes is always present your agreement must include a place to cover how any disputes will be handled. This way everyone has already agreed to how these disputes are to be taken care of and cannot argue the point and cause further problems for the rest of the members of the venture. This may end up being the most important area of your agreement and should be filled out very carefully to avoid any possibility of a legal challenge.
You can pay a lawyer to draw up this agreement if you are a large company that has a big enough budget to cover the costs, but this is not necessary as you can do it for yourself. You can of course write out your own agreement using one of the many different templates that are available for download online. Both of these documents are completely binding in a court of law, the difference is the amount of money you are going to have to spend. Each of them must be signed by both parties and in many states notarized in order for them to be legally binding.