Limited access to server 2003

I have a Windows Server 2003 SP2 machine that cannot be pinged. It can be browsed to on a limited basis by XP clients but not system 7. the XP box can connect to the shares but not see any of the files located in the shared folders with one exception. If I create a new file I can save it to the shared folder and then access it. I cannot check the firewall because I get an error when I try to access it. The error says that ipnat.sys is in use even after disabling and or reconfiguring RRAS to not do routing. I am using a single NIC. Any help or suggestions would be greatly appreciated.