Yes, digital cable from a box allows you to get digital channels you cannot get from an analog tuner. BUT whatever you can get on your tv without the box, that's analog and that's what you can still use your 250 for. The 250 also has s-video and you can connect the output of the digital cable box to get those other channels you can't get from the analog tuner. s-video don't use the analog tuner at all.
I don't know for sure but i think the 250 can use a minijack ir to control the cable box. Nope doesn't look like it. YOu can get a USB-irt and BTV will control the box through that.
HDHR:
http://www.silicondust.com/