What is the client trying to accomplish with network performance management?
You want to ask the typical reporter questions: who, what, when, where and why. Understand what is causing the client to ask about network performance, why they need it and what they've heard about available products or solutions. Get a handle on the client's needs and expectations before digging into specifics about the project itself.
I generally hear two kinds of responses from the client. First, expect a vague statement like, "My network runs slow" -- which is one of the main reasons why we talk about network performance. Second, you'll hear about a specific incident that has occurred that makes the client worry about their network. A common example is YouTube management.
For example, a client may discover that their employees are spending too much time watching YouTube videos, consuming precious network bandwidth and storage, along with work time wasted because the employees aren't doing their real jobs. When you factor that resource drain with another business-critical external service like Salesforce.com, which also demands WAN and LAN bandwidth, it's easy to see how everyday business can be impaired by poor network performance. It's a matter of figuring out where the real need is coming from.