Problems with Inline style in image captions

Hi everyone,
I am making a wordpress site and I love the fact that everything graphic is controlled by css.
BUT…
But if I upload an image and I set it to be left aligned and with a caption the worpdress engine automatically sets the box with the image to a certain width:
class="wp-caption alignleft" style="width: 310px;" -

I don’t want every captioned image I upload to have this 310 box around, also because it is often largen than theimage itself, screwing up my layout… ??

Any idea?