if I understand correctly, it's the DVD that has only 1 scart?
if so, might you have a spare scart on your TV?
probably the easiest solution, use your TV remote to select whatever input you plug the DVD into - if the scart is not marked up on your TV the easiest way to find it is to play a DVD and scroll through the inputs until you locate the DVD playing (your TV remote should have a button marked "AV" or possibly even "Input").
if no spare TV scart input, try sticking the TiVo on standby and plugging the DVD into the TiVo scart and see if it passes the DVD through.
now, if it's a DVD recorder (though I don't think you'd have a recorder with only 1 scart) that's a whole different deal - let us know what your setup is and we'll chime back in.
DVD has scart. TV has 4. When I only used to use TV and dvd, hook up was scart to scart TV and dvd. Aerial through DVD to tv. The guide with the dvd player says if set top box, to hook dvd player to that. I assumed tivo might be the same but it only has the scart currently plugged in to tv. Really fed up as never had anything like this before. Treated myself when I moved to my new place. Paid money for the virgin engineer to come and set it all up but he wasn't remotely interested in my dvd set up. Yet it is the key part for me. I have a large collection and I watch them a lot!