Need advice on what to ask when a new software client will visit us with an ideea for a new project?

Okay. So this new client will come visit us next week. Something about a big project, involving mobile devices, serial communications with some sensors, etc, etc, etc… Can’t really describe too much because of confidentiality clauses, etc…

I would like to know, is there a generic protocol defined for such cases? I mean, can anybody tell me what key questions we should ask him? For example, i think it should help if we know how does the actual system works, what are the drawbacks, what should they expect from the new system and things like that..

Thanks and sorry for the elusive description…