I have a buddy in San Diego that does stone care (although that doesn't help you
) but I would highly recommend using a pro if you know and trust one. However, if that's not an option I would try using Brightstone's Marble Refinishing Kit ([url=http://www.brightstn.com]www.brightstn.com[/url]). I pulled this from their site's FAQ page:
4) What is the difference between a stain and a white etch mark?
A stain is due to material that penetrates into the stone to cause a color change. For example coffee may produce a brown stain on light colored marble or granite. These stains can be removed by using the Stain Remover. Etch marks are caused by acidic materials or hard water deposits that marks the stone white or dulls the stone surface. This is caused by fruit juice, soda, vinegar, acidic cleaners, and
urine on marble, limestone and travertine. These etch marks and dullness can be removed and the polish restored with the Marble Refinishing Kit.
Hope that helps!