Yeah, your navigation is sensitive to the content, because Dreamweaver makes such extensive use of layout tables. Tables can apply a great deal of uniformity and a nice clean look, but this is a typical problem.
Your header is much more stable, again a typical feature for a table-based webpage. For this project, my recommendation would be to use a horizontal navbar as part of your header. That will give you much better control, and a much more uniform look to your webpage.
That said, there's no reason you can't make it stay where you want using CSS. However, it looks like this site is basically built. Redoing it with CSS would mean starting from scratch, so I'd recommend going with a more standards based layout. Dreamweaver has an excellent code view processor. It autocompletes a lot of things for you and you can configure it to autoclose tags. Really handy. But that's not something you learn in many Dreamweaver classes, since so many of them are about using all the fancy panels and drag and drop stuff in Design view. They seem easier, but you run into exactly the kind of problem you're having and there's no great fix for it. Design view just doesn't give you very good control.
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