Not "a" Black Widow. She's not actually a deadly Australasian spider with morbid sexual proclivities. That'd be ridiculous, and surely someone would have puzzled it out before now, presumably on her first casting session where the subject of her having eight legs and fangs dripping with deadly venom would surely have come up. No, Scarlett Johansson's reprising the role of "the" Black Widow, one of those superhero types, in that upcoming film The Avengers. Which is nice.
We can't believe you thought she was a spider. Look at her
We can see here that Scarlett's jogging around with Captain America and, um, some dude. Presumably he has superpowers too, because he's carrying a bow, and only someone with superpowers would be daft enough to do that. We don't know who he is. Much of our experience with comics started with The Beano and ended with a dusty, unread copy of Frank Miller's 300 that an ex-girlfriend thought would make a suitable birthday gift.
The Black Widow tends not to go in for the whole 'actual superpowers' deal, instead taking the Batman route of 'being so good at hitting people to the extent that superpowers become largely irrelevant'. Unlike Batman, Black Widow exploits a gap in the pain market by carrying around a shedload of guns - these allow her shoot people who are slightly out of range of her deadly fists rather than leap off tall buildings with her cape flaring out behind her or chuck pointy bits of bat-themed metal at her foes.
Batmen: Making things more difficult than they need to be
Wise indeed. We always thought the heroes who carry loads of guns, rather than those simply lucky enough to have been bitten by a radioactive whatever, were the ones we should look up to. Peter Parker's bitten by a spider and gains powers that he's forced into using to protect New York, in an angsty emo sort of way - The Punisher decides that he's had enough of whatever it is that's pissing him off and rocks up with a trunk full of firepower to solve the situation. That's something any of us could do. Well, if we lived in America, anyway.