Hi
Press Start on the Vista Machine and in the search box type Network. In the results, click Network and Sharing Centre.
You will see a list of things you can share on the Network.
You will see: Network Discovery
File Sharing
Public Folder Sharing
Printer Sharing
Password Protected Sharing
Media Sharing
Check these individually and set them according to what you want to do.
Under the Globe that says Internet on the main Network and Sharing Centre window, you will see a Customize link. Click this and set your PC to Private and click OK.
Hope this helps