Yeah you will need to switch to a different (the DVI or Component) connection for HD viewing and them to the RCA/Svideo (Use Svideo) input to view Tivo.
I ran this exact setup for awhile with 1 added step. I split the cable before it went into the STB and ran the extra coax directly to the TV. This way when Tivo is recording I could still watch basic cable and change the channel.
What your going to find annoying is if you have Tivo recording alot of things you won't be able to watch Live TV which includes HD TV without cancelling what Tivo is recording so you can change the channel.
My Solution to this was to get a second SD cable box (4-5 bucks more a month and after all this money, Big Deal!)
So since your not runnning video through an A/V reciever what you would do is....
Take Coax 1 after the spliter and run it to the HD Cable Box, Component/DVI out to the TV on input 1. Done.
Take Coax 2 and run it to the SD Box, then out via S Video/RCA to the Tivo, then through your DVD recorder and then to the TV on input 2.
This way you can watch whatever you want on the HD box at any time with out affecting Tivo! Tivo has its own Cable box to record and change channels whenever it wants and you never run into a conflict and can always watch Live HD TV if you wish.
This also fixes another issue, the HD Comcast Boxes do not have a serial connection so I had to use IR immiters which SUCKED. The SD boxes DO have a serial connection which ensured It didn't pick the wrong channels and they also changed faster if you were surfing the TV through the Tivo.
Just make sure that you tape over the IR sensors on the front of the SD box so when you change the channel on the HD box it doesnt change the SD box as well. Comcast has them on the same frequency.
Have fun.
Next you'll be asking about Universal Remotes so you don't have to keep track of what the hell is on what.
Its nice to press HDTV or Tivo and have everything turn on and switch to the right inputs. It makes it very easy for non-HT people in the house.
