They say there's no such thing as a free lunch and there's more than a grain of truth in that.
You may have done this already but is there any 'catch' in the Talk Talk offer eg minimum contract term 18 months or anything like that?
I changed from BT to Talk Talk for my landline but have kept the line rental with BT. The reason being that BT's enhanced Callminder will send a text message to my mobile if a message is left on the landline. I can then access the message from my mobile. If I changed the line rental to Talk Talk, this message facility would not be available - at least it wasn't when I first joined Talk Talk!
This is just an example of how careful you have to be before making changes. Another thing to be aware of is your email address. You could probably keep your Tiscali address and access it via webmail but, again, it would be worth checking before you make the move.
Best of luck!