Check out http://www.afp548.com/filemgmt_data/files/Leopard%20Server%20Quickstart%20Guide. pdf . This guide is pretty well done and allows you to get a server up and running in a matter of hours. I strongly suggest you check out http://manuals.info.apple.com/en_US/Getting_Started_v10.5.pdf too. Just get in mind you'll always use it in Advanced configuration, but things are not that bad.
Hope this helps. Good luck!