Sorry this is a late response, but I just realized something. If you have Comcast cable, then this might help.
A while back, our non-HD cable box started flaking out. We called up Comcast and they said they'll send a different box out. When the new cable box arrived, it was a spiffy brand new one, never touched, and still had the plastic you have to peel off. It had HD outputs on it including HDMI. I was concerned that they accidentally added HD service to my account (which we did not want to pay for). Anyway, I hooked it up with a single HDMI cable to my brother's 65in Mitsubishi. All the standard definition channels come through and the HD channels say that you need to order HD service. Perfect, exactly what I wanted.
If you can find a way to get that newer cable box (with the HDMI) without upgrading to HD service, then you'd be all set.