Jeff Cornwall has written an outstanding post about chosing whether or not to take on a partner:
A practicing physician who is in the early stages of planning the start-up of a new venture serving the medical field recently asked me about one of the most important issues an entrepreneur can face. While he has medical expertise, he believes that he will need some help from someone with more business and start-up expertise. How and where does he go about finding someone to team up with?
The specific questions you need to address in this type of situation involve the “Why?”, “What?”, “How?”, and “Who?” issues for building your team.