Given the number of column inches devoted to what she wears and who she's with, you could be forgiven for forgetting that Sienna Miller is not a professional celebrity but an actress.

This week she has the chance to remind us of that with a meaty lead role in 'Factory Girl'. Opposite Guy Pearce as Andy Warhol, Ms. Miller plays Edie Sedgwick, the rich-girl-turned-It Girl who joined the circle surrounding that high priest of 60s pop-art in his New York loft known as 'The Factory'.

That's the kind of fuss which you'd imagine the real Mr Warhol would have relished.

Like the people and times it portrays, this new film has caused something of a stir. The presence in the script of the guitar-playing, harmonica-blowing music star who's played by Hayden Christensen rattled the cage of lawyers acting for Bob Dylan. And the source of ultra-reliable information that is the internet has been buzzing with rumours that a love scene in the movie went far beyond method acting, if you know what I'm sayin'.

I'm a little puzzled by the apparently never-ending fascination which Andy Warhol and his circle exercise over authors and film-makers, and that bemusement was only partially eroded by 'Factory Girl', though it's a film with significant strengths.

The most obvious of these are the two central performances. As the self-styled poor little rich girl Edie Sedgwick, Sienna Miller projects real vulnerability and neediness, while Guy Pearce delivers the most memorable and convincing of the many film incarnations of Andy Warhol - opportunistic, self-absorbed and completely shallow, but all the more darkly fascinating as a result.

The movie also succeeds in getting across the idea that this was a pivotal time in modern culture, when the traditional privileges conferred by inherited wealth and social status were being swept away by the concept of fashionable celebrity.

But that's really as far as its insights extend, and I don't think that's because director George Hickenlooper was trying to make some ironically superficial statement about superficial characters. He just can't tell us any more as a rather clunkily structured film moves forward. And the movie's limitations are all that's revealed by the ponderous romance between Edie and the singer awkwardly played by Hayden Christensen.

To sum up - an average film lit up by the splendid work of Sienna Miller and Guy Pearce.