In order to answer your question in details, and not just in a general way, we would need to know more about your project, situation, etc.

First of all you need to understand "why" you are meeting with the client!  What is the purpose of this meeting?

For example:

• Is the purpose of this meeting to discuss the Vision of the document?
• Does the Vision, Business Case, and Project Charger exist and you are now ready to elicit requirements?

You also need to understand the "state" of the project!

For example:

• Are you adding creating a brand new system to support existing business processes?  If so, are these processes already documented?
• Are you replacing an existing system? If so, any documentation exist for the existing system (requirements, functional specifications, user guides, etc.)?
• Are you modifying an existing system? Again, are there any existing artifacts which describe the existing system?

You need to understand the "methodology" used on your project and in your organization!  Do you have a published process?  Can you manager guide you?

For example:

• Are you operating in an Agile process where you will have direct access to the stakeholders during the development process? if so, you might not need to capture/elicit too much upfront as many of the details will come up via subsequent iterations.
• Are you in an environment where requirements must be all documented upfront in details, using a specific type of artifact, and signed in blood by the C-Level Executives?
• Somewhere in between?

In general, as long as you are somewhat prepared for the meeting (and you say you are) you'll be OK.   Just make sure you have some high-level open ended questions that you can ask and then be prepared to be quiet and listen.  I used this technique many times with success when I did not know much about the system, process, business.  This works because is 99% of cases there is one or two of the stakeholders who love to talk and they will gladly (and unknowingly) take over your meeting and elicit requirements or at least uncover information for you that you can piggyback on when continuing these client sessions.

- Adrian