Bruce,

You're right, Microchip\MPASM Suite wasn't in the PATH. Now all is well, I think. Except that somehow I screwed up MPLAB so I wasn't able to modify my .bas file. It said that it couldn't find the old file in SaveAs or some such goofy thing. So I made a new .bas file and was able to compile it in MPLAB and program the chip. Hopefully no other goofy problem will show up.

I don't understand why the PATH wasn't set up properly. Maybe some problem in the MPLAB install?

Many thanks to you Bruce and to the others who gave me suggestions.