TinyMCE image float, automatic set margin
If the styles WYSIWYG button shows image right or image left try applying that and save your edit. If that applies ok you can use Firebug to see the CSS class it adds to the image and just alter the css rules to your needs.

Or else, you can supply your own css styles to a wysiwyg profile. They are typically of the form:

wysiwyg_option_name=css_class_name

for example:

ImageRight=img-right

you then make an image right class in your themes css file:

.img-right { padding: 0 0 5px 5px; }

I believe both TinyMCE and/or the WYSIWYG module both support these features.