Thanks for the replies the green dsl light stays a solid green so I tried looging onto the net via the ethernet cable to the hg612 using the username and password I grabbed from wireshark have I got this all wrong thing I can connect to sky fibre through the hg612 only I get error 651. I can't get my head round it never mind the n66 part of it I just seem to be reading the same posts and getting more confused.
again thanks for replies and I shall soldier on until I crack it.
The username and password you extracted via Wireshark will not work with any connection you attempt to create on either the HG612 or from your own computer. The ID and password can only be used when submitted as part of the DHCP request. It's a very proprietary way of authenticating. As a result most routers do not support this. Even the RT-N66U doesn't with the Asus standard firmware. However, it does support it if you use the Merlin firmware. To me it sounds like you've done the hard part by using Wireshark to get the ID and password.
The only way you'll be able to connect to Sky without using their router is to leave the HG612 in its default configuration. If you've made config changes to it I'd recommended factory resetting it. Then flash the Merlin firmware onto the RT-N66U (do a factory reset after flashing the firmware), and then set-up the internet connection on the RT-N66U and use the extracted ID and password in the clientID section of the WAN configuration page. Once that's done you should be on-line.
Sky don't want you using your own router, and they've made it deliberately difficult to do so. It also goes against their T&C's.