There are a couple of ways to do this. The first would be to go into HTML source mode and wrap your image widget with a DIV that had a style of float:left. e.g.
<
div style="float: left">
<innovasys:widget layout="block" type="Dynamic Image">
<innovasys:widgetproperty layout="inline" name="ImageTitle"></innovasys:widgetproperty>
<innovasys:widgetproperty layout="inline" name="ThumbnailURL">
Images/ScreenCap_thumb.png
</innovasys:widgetproperty></innovasys:widget>
</
div>
<
p>Just some text to wrap around</p>
You could also create a copy of the image widget and add the style="float: left" (or right for text on the left of the image) to the widget definition HTML.
The only caveat is that the text does not show as flowing around the image whilst you are editing (because of the way that widgets work at edit-time). The generated output or preview will be correct though.