I don't think you can transfer the lifetime to a new box. If you could, I'd be set.
There have been periods (as early as this past year IIRC) where Tivo charges a fee for you to transfer your lifetime to a new box. I would call Tivo and check. I couldn't google anything current but that doesn't mean it isn't possible.
Alternately, you can do what I do. I transferred a lifetime Tivo subscription to a Series 3 a few years ago when it first came out, from my HD DirecTivo. (Yes, I paid a lot but it was worth it.) Then I got a Series 2 DT for another room. I pay a secondary fee of about $5/mo IIRC for the 2nd Tivo because I already have lifetime. Yes, I pay another fee but my wife watches her shows on that and I record all my HD shows on mine. Everybody's happy. IF you can't do a transfer, you could keep the lifetime on your existing box and buy the cheapest Tivo HD you can find. Then pay the extra Tivo fee for the Tivo HD.
Cable cards on Comcast shouldn't be more than $1.70/mo. The CS reps won't tell you that but that is the fee for the card rental because you don't need the cable box anymore, which itself is $8/mo. With a Tivo HD, you only need one card if you get an M Series card, which Comcast does carry in the Bay Area.
