When talking things with a prospective investor (a venture capitalist, perhaps, or a friend with extra cash to invest), it would help if you already have a company incorporated specifically for your intended business. Or at the very least, you should have already have a holdings company incorporated for the purpose of managing your business endeavors. Otherwise, it would be a bit difficult for your prospective partners to trust you.
Business is best dealt with trust. I’ve seen instances of longtime friends having quarrels because of failed business plans and endeavors, and in most cases the problem lied in either party’s not having enough commitment in the business. It had mostly been due to the fact that the plan’s all up in the air—nothing concrete had been done yet, save for some projections on paper.
So at the very least, start with a corporation, so you have a solid, legal entity to represent when dealing with investors.