http://www.faqs.org/docs/Linux-mini/Linuxdoc-Reference.html

http://tldp.org/HOWTO/Howtos-with-LinuxDoc-5.html

LinuxDoc is a lot easier to learn than DocBook. But most of what you learn about LinuxDoc would also be useful for DocBook. So if you eventually decide to go for DocBook, most of the effort spent on learning LinuxDoc will not be wasted.