There are a few things you should note regarding floated boxes. For one, the box being floated should have a width defined for it, either explicitly or implicitly. Otherwise, it will fill its containing block horizontally, just like non-floated content, leaving no room for other content to flow around it. As such, floated boxes are always treated as block boxes, even if they are defined using inline elements.

[1] http://www.brainjar.com/css/positioning/default3.asp