Getting kind of crazy here.
My network is made of 1 desktop PC (XP Pro SP2), one wireless notebook (Windows Tablet PC SP2), one Xbox, one Xbox 360 and one Squeezebox 2 (Slimdevices music streaming device).
The desktop connects to the internet through a small hub on a residential network (fiber optics cabling throughout the city, Milan, ISP is Fastweb if somebody is familiar with it). The hub provides DHCP and assigns IP in the 1.39.ABC.xxx range. At the same hub I connect a Wi-Fi Access Point, and the Tablet PC gets its IP from the hub too, always in the 1.39.ABC.xxx range (I put ABC for privacy reasons, it's a regular number).
Xbox, Xbox360 and Squeezebox connect to the network through a shared Internet connection. The desktop PC has two network adapters and the second one is used to create a local network in the 192.168.0.xxx range. All three devices connect to the internet without any problem, even with the XP Firewall activated, nothing wrong with the 192.168.0.xxx network for what I need.
The problem arises because, although I have the exception set for File Sharing, as soon as I activate the XP Firewall on Ethernet card #1, the Tablet PC can't see the shared folders on the desktop PC.
Both machines are on the same workgroup, the Tablet PC can ping regularly the desktop (with the firewall activated too), it can even use Remote Desktop on it. But no shared folders. If I open the workgroup I see the desktop machine, but if I double click on it, I get the message "COMPUTER 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. The network path was not found."
I've given full permissions to EVERYONE on the folder I'm trying to share.
[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Lsa] sets everyoneincludesanonymous to 1. restrictanonymous is set to 0.
Without the firewall on Ethernet card #1, file sharing works fine.