The important thing when making floating divs is to set the "float" and "width" attributes.
<div style="float:left;width:100px">Left Div</div>
<div style="float:left;width:100px">Middle Div</div>
<div style="float:left;width:100px">Right Div</div>
<div style="clear:both;">Bottom Div</div>
Would generate:
==============================================
| Left Div | Middle Div | Right Div |
| | | |
| | | |
| | | |
| | | |
==============================================
| Bottom Div |
==============================================
If you resize your browser to a smaller window, the divs will wrap. This is the default behavior.