How do I know if my idea for a business is a good one?
If the business is never going to make money, then you take a public good path toward raising seed money. You find a large organization, either government or foundation or something like it, to donate money to support the cause.
If the business is going to make so much money that it can offer an interesting return on investment for outsiders who invest in it, then you're on an outside investment path and looking for either friends and family investors, angel investors or venture capitalists. Try this chapter (http://www.hurdlebook.com/default_Left.htm#StartTopic=Following_Up/Getting_Financed/Getting_Financed.htm|SkinName=Default) of my free online book on business planning for a summary of how to raise investment money. Beyond that, there is a lot of information about that on this site, and others, like www.bplans.com.
And if the business is going to make money for you, the owner, but never enough money to make it an attractive opportunity for an outside investor, then you're looking at borrowing money. That's tough these days because of the financial crisis, but will open up again when the time comes. That starts with the SBA at www.sba.gov, and your local bank.