Built-in KDE method. i.e., through the KDE control center.
After reading your post, I played around with my wallpaper. I set it to 'no background,' then I set it back to the one I had before. Afterwards, I switched gkrellm themes and it became transparent again. Finally, I closed Eterm, opened it again, and it was transparent.
Everything seems to be OK now. Thanks for the push in the right direction.