I hve the DNS problem on my Windows 7 and have been in SL a whole and just got the problem today.
I can go to any website
I did everything you said in your post:
Contacted my DSL provider - they said no problem
Cleared the DNS cache in Windows 7
Unpugged, shut down for a while, Restarted
Even set the Google DNS settings lke the Wiki recommended
Keep getting the same error and cant log in