Thank you for having used the search feature here
As you saw, there just doesnt seem to be any one solution fits all, regardless of their connection type, and many are on cable or dsl. All we can suggest is trying what others have found works.
-disable xp firewall
-use a diff server port other than 6667
-try connecting to server ip rather than domain
-check router firmware/drivers
-in router, configure your TCP and ICMP aging in your Masqudaring options and set them higher than default.
-some have found relation to certain nic cards
Do i understand correctly that in your case it just started happening after you reinstalled norton?
What OS are you using? any router?