As long as the TV supports 480i resolution (which AFAIK all sets do) it will work. You will get a 4:3 picture with "pillars" (side bars) and can use the TV's stretch mode(s) if you want to fill the screen. I would advise using the S-Video output from the SD STB as it will provide the best quality signal for SD.
Also, if it has a QAM tuner you should be able to get the local SD, local HD, music, and PEG channels.
