The Wiki component in Leopard Server is designed to be ready to run and use for all your workgroup needs, but for those who need to customize the look and feel of their Wiki environment may find a new article on creating custom themes helpful: From the article:
Wiki Server, a part of Mac OS X Leopard Server, provides this wiki functionality to all users with access to the server. Individual groups can tap into Wiki Server to create their own wikis and customize the look and feel of the wiki to suit both their content and audience. By creating their own personal wiki theme, Wiki users can apply their own style and identity to the wiki, in addition to supplying their own content.