I have the same sort of problem with an Xp machine.
Although I have not found the answer yet one thing you coud try first is to ping it from another PC.
You will need the IP address of the vista machine (open a dos window and type ipconfig) the on another machine open a dos window and type ping 10.0.0.2 (or whatever the address is) and it will tel you if it can contact an get a response from th vista pc.
Or you could search for computers from explorer and put the ipaddress in the search box and try to connect that way
If not then I would of thought that some firewall is causing the problem.
If you can then connect I hope somebody else has the answer