Adding css class styles to images

I have a page template created with css that I would like to allow my users to add images, and based on the style selected, have the image appear to the left or right of the text. Is this possible? I see that when I insert the image into the page, it applies a <p> tag, but when I select the image in Contribute Edit mode, the styles list does not display so I'm stuck with an image in the middle of the page with text only above and below. Any words of wisdom would be appreciated. Even to know it can't be done.

Thanks!