Hi Jamie,
At this stage, it's just your billing that's changing. You'd have to call the TalkTalk sales team to be put onto the TalkTalk LLU equipment because at this stage you're still on Tiscali equipment. We'd effectively add you as a new customer if you go this, so you get a new provisioning and a shiny new D-Link N router with the Pro pack. Any contract you're in at the moment with Tiscali will be waived ofcourse. Your email addresses will be an issue though as most people lose their @ Tiscali.co.uk email addresses. I don't work for the Tiscali partition, however I have heard that if you set up a dial up account with them using your email address then it will remain live after you close your broadband account. Obviously you'd never use the dial up account and it would be free.
Still, @talktalk.net email addresses are available. It's not ideal and it will be an inconvenience, but we are unable to retain the email addresses any other way.