Link Layer Topology Discovery (LLTD) Responder (KB922120) for Windows XP

This package contains the Microsoft Link Layer Topology Discovery (LLTD) responder. The network map on a computer running Windows Vista shows a graphical view of the computers and devices on your network and how they are connected by using the LLTD protocol. The LLTD responder must be installed on a computer running Windows XP before it can be detected and appear on the network map. After you install this item, you may have to restart your computer.
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News Source: www.microsoft.com

Interesting comment also:

It does not work correctly
The bad thing is that it does not work correctly – have tested 6 computers on one switch and Vista draws absolutely randomly 4 PCs on one switch and 2 pcs on another, next reload (F5) 6 PCs on separate switches, next reload 3 + 1 + 1 + 1 etc.
(Vista RTM + XPSP2 were used)
The restart is not needed.