Does mixing Windows XP and Windows Vista on a network matter?

Vista uses a new technology called Link Layer Topology Discovery (LLTD), which is something that Windows XP does not have. If you want Windows XP to show up on the Network Map, you'll need to download the update that Microsoft has available.
Here's how to install the update:
To install the LLTD Responder to a computer running Windows XP
1. Download the update for Windows XP from: http://go.microsoft.com/fwlink/?LinkId=70582
2. Run the update on the computer running Windows XP that you want to appear on the Network Map.
3. On the Software Update Installation Wizard, click Next.
4. On the License Agreement page, read the license agreement, and if you agree to the terms, click I Agree, and then click
Next.
5. On the final page of the wizard, click Finish.
6. If you are prompted to do so, restart your computer.
7. After your computer running Windows XP restarts, generate a new Network Map with the computer running Windows XP included.
For further information visit here.