Thanks very much for the help. I did everything you said:
1. Plugged in well: check.
2. Rung out cord: Both RCA prongs are connected to miniplug tip, both outer RCA electrodes to miniplug shaft.
3. BD Setup ok, I think.
4. Speakers work fine when connected to laptop.
5. Audio plays correctly when BD connected to TV via RCA.
I think I have the wrong adapter (thanks Radio Shack). I didn't notice before that the miniplug end of the adapter only has 2 contacts, while the cord I use to connect to the headphone jack of my laptop has 3. I am completely ignorant as to how the stereo information is encoded, but it seems to me that tying the left and right speaker outputs together negates the "stereo" idea. I will try to find an adapter that has 3 contacts on the mini plug end and doesn't tie the two RCA prongs together.
Thanks again for your help. If I'm on the wrong track, please post to say so. Otherwise, it's back to Radio Shack asap.