Without a CableCard you should be able to tune the SD digital channels and any HD ClearQAM channels on the cable. You can tell the Tivo that you do not intend to install a CableCard and have it download Guide Data based on that. Unfortunately, if I remember correctly, all it assumed that I could get when I tried that was the analog versions of the cable channels even though my digital ones are not encrypted. Bottom line is that I had to manually input the digital channel number and, of course, had no Guide Data for it.
"I'm just one story in a two story town." Bon Jovi