Adding extra divs and switching stylesheets…

Alright, I’ve been using wordpress for about 10 months now, but I’ve always added my entries to my layout using an Iframe because I was so scared of messing up my index page until recently. Now that I’m more confident with all that, I need to add some extra divs to the index.php file. Would I need to do anything special? Or just simply add-away, lol? I mean… will adding a div layer for say, navigation, screw up the blog?

Also, I really would like to have skins, where a visitor can choose a theme. I have been looking at this tutorial: http://www.alistapart.com/articles/phpswitch
I just want to be able to switch stylesheets. That’s all. I don’t want to fuss with headers & footers because I’m not really ready to take that on, although i use them at my collecctive: http://pink-pistol.net/linkage

Would I be able to have different stylesheets with wordpress? I’m kinda confused. I wouldn’t know where to put all that stuff I read about in the tutorial… could anyone help me out here and explain to me if this whole mess would be easy or difficult, impossible, etc?

Thanks,
Ashley
http://pink-pistol.net