So, this post is here mostly for the benefit of web searchers :-) I googled for a steampunk widget theme for my N900 and found nothing. I tried “steampunk theme n900”, then replaced n900 with maemo, hildon, freemantle... nothing.
Then I tried a few promising-sounding ones and, by trial and error and luck, finally got to IivilSteel Black And Gold, which just rocks.
So if you got here while searching for the same thing, now you know.
(I guess now I need to go make a tag icon for steampunk... maybe one for the n900 too)