Smoke

You don't. You make a picture that ends in that extension. Although you could always change the extension on a .html file with file renaming. If you wanna do the rotating sig trick, you need to do a bit of PHP coding(Ginnsu has something like that in his sig, displays random quotes from the Quotebot), not HTML stuff.

Nope, that's definately the Brinstar theme. Plays when you first enter that area. Fire up your copy of Super Metroid and go check.