5
Here are a couple places you can get documentation on how to edit your themes:
Xoops For Dummies @
Xoops Documentation SiteXoops WikiIf you really want to trick your site out, spend some time learning html and CSS. Here's an excellent resource for learning the basics of coding.
W3SchoolsCreating XOOPS themes is very similar to coding traditional html/css themes, except you have to include some php code to get things to display correctly.
My best suggestion would be for you to open /themes/default/theme.html and /themes/default/style.css in a text editor and study the code. Compare it to what you find at W3Schools. If you pick things up relatively quickly, you could be coding your own custom theme in less than a week.
Hope this helps.