Learn CSS positioning in 10 Steps
http://www.barelyfitz.com/screencast/html-training/css/positioning/
Default positioning (static or unspecified) is all you need for 98% of layouts.
"Drawing boxes" in DW is not a good way to work either. DW is not a graphics editor like Photoshop. It's a web authoring tool.
When you draw & move APDivs on your workspace, you remove content from the normal document flow and position them relative to the top, left corner of browser window or the nearest relatively positioned parent container.
When you preview the page in browsers, everything falls apart. APDivs are not a good layout approach. Here's more on why:
http://www.apptools.com/examples/pagelayout101.php
Nancy O.