Thanks so much for your responses!

Hmmm.  I have never noticed this before, but I guess I usually have something else in the background or am rendering animation.  I think the problem with rendering to JPEG is that you loose some detail in the compression.  PNG is a lossless compression, so I prefer to use it.  I wish I could just check a box somewhere in Poser that says "don't make the background transparent."

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