This is a pretty thought subject and unfortunately there is no visual way to do this.

1. You need to get familiar  with templates
msdn.microsoft.com/.../tsovIntroTemplates.asp

2. Topics template  are nothing else than WSS templates  that only applied to Topics

3. The template list for Topics are contained in the webtempsps.xml file located in \TEMPLATE\1033\XML

4. From this file, you can find the sub-dir name for the Content Area template -> SPSTOC

5. In the directory TEMPLATE\1033\SPSTOC, locate the file XML\onet.xml, this file contains the definition of the template and how it is provisionned. Making changes will involve making additional changes in this file and other files and directory

6. In order to create  a new template, you will need to clone an existing one and add it to the WEBTEMPSPS.XML