One of the biggest differences between Home and Pro is the ability to network. XP Home won't even connect to a domain. That isn't the problem here as you don't have a domain. It is also limited in the number of connections TO it compared with Pro.
Given, that you can connect otherwise, this is probably not the issue. The issue, in my best guess, is a firewall issue. As stated, it is nearly always firewall.
Again, I would remove Norton immediately. I would remove Norton anything off your machines. If the others are working fine and they have Norton, then I would leave well enough alone.
If all this fails, after you try reinstallation of the program (after all other steps), if you have XP Pro or WIN7, I would start over and install it WITH the Windows firewall only by default.
I also hope that the main computer is not running Home.
