You can find the jForum templates (skins) for 2.1.x under the templates/default directory.
The first place to start is the styles (css info) and images directories.
The next place is to look at the htm files. A good place to start here is with the "header.htm" and "footer.htm" files. These define the html stuff that "wraps" all the standard jForum.
To dig even deeper into how the templates work, I'd suggest looking at the
http://freemarker.sourceforge.net/ site to learn the template syntax and going from there.
FYI - The template names more or less match the jForum functions being requested. You can find out more by digging in the code, but generally just veiwing the source of the page you want and then finding the matching HTML in the page names that seem to look right works too.
Greg
[originally posted on jforum.net by monroe]