http://www.kitz.co.uk/isp/talktalk_connection.htm
http://www.pjls16812.pwp.blueyonder....alk/index.html
At one time, it seems TalkTalk had an unexplained change from using PPPoA VC-Mux to PPPoE LLC-Mux
Not sure if that change is still in effect, or applies to some circuits and not others - if one doesn't work, try the other, great for confidence - NOT!