Can I use Tivo Series 1 with HD receiver?

I'm considering upgrading my D* service to HD, but I love my old (highly modified) Tivo and want to continue using it for recording shows. Since the new HDR20 seems to have lots of bugs I'm inclined to go with an HD receiver and continue using the Tivo -- provided the HD receiver is compatible.

My question is this: is it possible to connect a Tivo Series 1 to the HD receiver for SD recording and control it like I've been able to do with my RCA SD receiver?

Stretching this a bit: would it be possible to use the HDR20 DVR in the same manner with the Tivo for SD recording? Does the HDR20 have dual tuners? That way at I'd have my reliable Tivo as a backup for shows that the HDR20 loses (or runs out of capacity, etc.). I'm ready to dip my toes into the HD thing but want to have the SD Tivo at least as a backup DVR.

Make sense? Thanks all!