I have one PC acting as a file server on a wired network via router with 10 other PC 's on this network. I upgraded the OS and PC to Win 7 Pro when the original system with Vista as OS had a hardware failure.
Now I can see all the PC's on the network but I can only use the PC's with Vista as OS to access the server files; those with XP display and error message that I need to have the network administrator permission to access those files. The desired files are in Public folders. I do not have a firewall up on any of the computers while I tried to access the files on the "server."

Any suggestions?

See if this helps: Share Files and Printers between Windows 7 and XP - How-To Geek