How do I check / add a trusted domain?

Having problems with iPhone Sync. One thing I need to check is that Norton isn't filtering out Apple programs. From Apple support "The following iTunes Store Internet addresses should be added as trusted domains to any filtering software that may be running:

  • itunes.apple.com
  • ax.itunes.apple.com
  • albert.apple.com
  • gs.apple.com"

How do I find out and if they are being blocked unblock them?