Why can't I see my Windows XP laptop in Vista's Network and Sharing Center?

I'm using Windows Vista on my two desktop computers and Windows XP Professional on my laptop. The desktops are connected to a router using Ethernet cables, while the laptop connects to the network wirelessly. If I open the Network And Sharing Center in Vista and click the link to display the network map, my laptop doesn't appear on the map, even though it's listed as being part of the network.

Connecting the laptop using a cable doesn't make any difference. Although this doesn't prevent me from sharing files between my computers, I just wondered what the reason for this problem was.

Phil Lambton, via email

Incompatibility between Vista and XP is at least partly to blame for this. The networking map feature of Vista uses something called the Link-Layer Topology Discovery protocol (LLTD) to detect other devices on the network and place them on the map.

While Windows XP PCs can be queried by the network map, it doesn't provide enough information for Vista to determine precisely how they are connected to the network. You'll be pleased to hear that there is an update available in the form of the LLTD Responder that you can install on any Windows XP machines that are causing problems. The update can be downloaded and should sort out your network map.