You're looking at a bit of a steep learning curve. To get you started with some tips check out one of my earlier posts: http://forums.asp.net/ShowPost.aspx?PostID=1134335#1134335

I still have trouble pinpointing which style affects which item. There are a couple of  "css wand" tools around that might help you out, but even those require some messing around to install and don't show all styles.

My favorite method arises from the fact that I install and manage DNN files and folders from Microsoft Frontpage. Open a page on your site in your web browser, view source, copy source, paste into blank Frontpage page and voila.. you can inspect the styles in the little bar directly above the viewpane.

Note: This does not work for Solpart menu styles and it works best if you are logged into your site using Frontpage whilst doing this... otherwise the styles and graphics won't all appear. This is also a great way to hack your skin around and make mockups using what you've made so far.

Good luck..

Rob