I just added a Vista machine to my network and am having the same problem, but I have figured out half the fix. I did 3 things in order to see my machines on the network from the vista machine.
1. upgraded my routers firmware (i did it just in case),
2. vista has a setting called private networking, I made sure it was turned on. If you search for private networking in vista help it links you to the spot to change it.
3. changed my networking workgroup from "workgroup" to mshome which is what the rest of my computers are on.
Now I can see the rest of my machines, and here is where I am stumped.
When I click on my vista machine, a little window pops up asking for a username and password. I only have one account on the vista machine and i did not set a password for it. if I just put in a user name it doesn't work. How do I create a user name and password that allows me to access the computer, without having to use a password locally on that machine every time i start it up.
Thanks for any help anyone can give