How do I prepare a non-disclosure agreement?

I meant to write "unenforceable" below, typing too quickly.  A non-compete, if overbroad (geographically or, in some cases, otherwise), has been held to be unenforceable in many jurisdictions.  

I agree-- not the kind of thing you want to do without a lawyer, especially if it can be construed as a non-compete, in which case, if it is overbroad, it may be enforceable.  You really need a lawyer to prepare these documents if you're at all concerned about enforceabilty and, should the party not comply, cease and decist and potential damages.  

You can certainly find sample or model non-disclosure agreements off the Internet and then modify them to your needs. However, this is  not recommended: since you want an agreement that truly meets the needs of your business and reflects the specifics of your industry, you should have an attorney draw one up for you. Sit down with the attorney, tell him or her all about your business and the possible transaction, and let him or her draft something specific to you and your company.

At this point, the non-disclosure is probably all you need, though you need to make sure it also states that you own any intellectual property (trademark, copyright, patent) in anything you share; that the disclosure is only for the purpsoe of evaluating the products or business arrangement; that the information may not be used for the client's own benefit or shared with others; and that at the conclusion, all information will be returned to you and copies destroyed.