Infranview isn't really appropriate. Doesn't matter anyway...with much help from SkinStudio on the IRC channel, I've found out which settings to use with PSP when saving a PNG to make it work properly.
File/Preferences/File Format Preferences...PNG tab...uncheck 'Load and save transparency from / to alpha channel
When you save your PNG, run the optimizer...under transparency tab, choose 'Alpha channel transparency'.
Optimize your palette if you want.
It will save as a 32-bit PNG. When you import it into SkinStudio it will be converted to a 32-bit TGA. Of course (and this is the part that threw me) not all buttons and so forth support alpha channel transparency...basically, if the transparent/translucent checkboxes are active, you're in business.
A HEARTY THANK YOU to SkinStudio fro all the help!