I'm not sure what you mean by more professional using css over html... it's really a combination of both. Those who use css like the handiness of having all pages refer to the css file to provide consistency to the entire site without all the work of having to code each individual page. However to answer your question:
Yes, you can use css to deal with layout, too. When using css in this manner, you assign classes to either the layers or table cells, whichever you prefer to use. In the css file where that class is define, you assign the graphic as an attribute of that class.
For example say you have a class called footer. For that footer class you define how your links display, the color of the text and how it is aligned, height, width, and so on. You can also add the graphic as a definition, either as just a graphic to be included in that class or as a background. Each class will have its own set of definitions.
I'm no expert in css yet but I think that's a pretty fair explanation. Any others who might know more, please come along and correct anything you see that is wrong.
