unable to map drive to windows 2003 share

I have Windows Vista installed in my computer and I am not able to map a drive to a Windows 2003 network share. I am doing this over the internet and it is working fine in Windows XP. Below is what normally works:

Mapping Vista to XP pro local - works
Mapping XP pro to \\IP\share - works
Mapping Vista to \\IP\share - network path not found

I have also made the lsa registry tweak and tried turning off my firewall but that is not working for me. Behind a server with ISA firewall is a Windows server 2003 but with the rule to allow netbios via to this server it works since the XP pro can map to it properly. Can anyone help me with this issue? Thanks.

Have you got any other security software on Vista cause it might be blocking the sharing. Or else, if you want to share a folder, then there are two places, you need to assign permission and that is sharing and security tabs. Share permissions must match the folder security for access to a share to be successful. Have you assign permissions in the Security tab?

I have Avast antivirus and Windows firewall running on my computer and permissions should be alright, as I am able to log in as Admin but after that I cant get far?

Do you use a VPN to connect to the server, if so then what VPN is it? Are you able to ping the server by name and by IP address, if not then are you getting the same errors from both side?