I had this problem: when I posted with an image that had wrapped text around it, the text sat right up against the image. It looked horrible. If I added Vspace or Hspace it would show up in Internet Explorer but not in Firefox.
My fix was to download the free program Windows Live Writer, which automatically connects to any of your blogs. You can write your posts in Live Writer and publish them directly over to your blog very easily. Also, in Live Writer you can add margins to all your pictures. It's also easier to format paragraph styles and alignments. This is a free program and integrates very nicely with WordPress as well as other blog apps. I highly recommend it, as it has saved me lots of time!