XP/Vista Networking
From GM Wiki
Problem:
XP computer shows up in Vista's network map, but you cannot click on it
Solution:
We've checked and accounted for firewall, services, ipv6, LLTD responder (KB922120), and "restrictanonymous" on the XP. I know from personal experience that it is possible to get corruption on an XP that we do not know how to fix short of a Windows installation. That's my guess at this point.
Two other things to consider/try. Non-Windows firewalls or security suites can result in quite amazing errors, so there is a slight chance of such a problem with one on the Vista.
I found somewhere (lost the source years ago) one other "corruption fix" that worked for a few people ...
Another: (XP Pro w/SFS, and probably Win2k Pro)
(on the XP computer) Start Menu --> Control Panel Double-Click Administrative Tools Double-Click Local Security Policy Click "User Rights Assignment" on the left panel Look for the top entry on the right panel listed "Access this computer from the Network" Right-Click --> Properties Click "Add User or Group" Click "Advanced" --> Find Now Select and press ok to add a User or Group. Add all of the following:
Administrator Guest Everyone NETWORK
Press OK two more times and you're done.
Refresh your network folder, and your network map; you should now be able to access your XP PC.
Original Source
http://forums.techguy.org/networking/823859-vista-xp-network-problem-2.html

