XP and Vista networking

Hello, I am having 2 computers at my home one is running on Vista and the other is on XP and I have started sharing of computer on both machines. Now I can browse through the XP computer while sitting on the Vista computer but when I click on the vista computer while sitting on the XP computer I get the following error message:

"\\computer name/user is not accessible. You might not have permission to use this network resource. Contact the administrator of this server to find out if you have access permissions.

Access is Denied"

Both computers are connected wirelessly to the internet through an unsecured network through a router. I have not put any password/WEP on the network. I have tried by switching off norton antivirus firewall on the vista machine but still it doesnt work. I am the administrator on both the computers. Any help will be useful. I have also browsed on the forums for the solution but I couldnt find anything that can solve my problem. Thanks in advance.