Fist of all turn off both firewalls and reboot each computer. Disable any firewall within the router. On either machine run the Network setup wizard from control panel. Then make sure that there is at least one document in each computers "shared folder". This should get the basics running but post back with any problems.
Make sure that the XP Pro machine is set to simple file sharing. Whereas the Home machine will be I believe this is not the case by default with the Pro machine. click here
If all works we need to turn on each firewall individually and fix any issues as we go along.