What's it all about, Sienna?

IT is a glamorous photograph of nine of Hollywood's most respected leading ladies and brightest hopes.

And Sienna Miller.

Quite how the 23-year- old, better known for her fashion sense than her acting abilities, won a sought-after place on the cover of Vanity Fair magazine's annual Hollywood issue remained something of a mystery last night.

Jude Law's fiancee is pictured in the fold-out section (not pictured) of the front cover of the American magazine's March issue, alongside such stars as Kate Winslet, Uma Thurman or Cate Blanchett.

But unlike them, she has had just one starring role, in last year's remake of Alfie - which flopped at the box office.

And she more regularly makes the headlines for her relationship with the star of that film, Jude Law.

She began dating the British heartthrob late in 2003 and they are now engaged, something which has raised her profile no end.

Miss Miller, who also had a small role in last year's low-budget British gangster film Layer Cake, is the daughter of a New York banker, Ed Miller.

She was brought up in England by her mother Josephine, a former model who was once secretary to David Bowie, with whom she had a fling in the 1970s. Miss

Miller, who was a model before turning to acting, regularly tops 'best-dressed' lists, and was widely credited for sparking last summer's rush for cowboy boots and ponchos as women flocked to copy her 'boho-chic' look.

Marks & Spencer also said she had inspired its bohemian range.

However, standing alongside some of Hollywood's finest, Miss Miller's limitations as an actress leave her looking like little more than a clothes horse with a famous boyfriend.

The only other British actress deemed high profile enough to feature on the Vanity Fair cover is Miss Winslet, for whom it is her third appearance.