Unless you know Java, then the chances of making a plugin are very hard. You have to know something about java, even the basics, to really get a good plugin going. I find that if you do not know what Objects are, or arrays, or classes, then it might be a bit difficult. While you don't need to have a complete understanding of java, you need to know some. If you can, look around at code that plugins have in http://www.github.com and use that to help learn truly about how plugins work. The guide is nice, but lacking IMO (and I have used it).
http://www.youtube.com/user/GTOTechnology has created a few videos explaining how plugins work, but they are a bit lengthy, but are very good resources. HOWEVER the issue is that Bukkit has stepped away from the resources that he uses, so you cannot completely rely on it, but using both the link above that jefe mentioned, the vids, and looking at other plugins and their code, and know something about java, plugins are not really that bad
http://wiki.bukkit.org/Plugin_Tutorial
http://www.youtube.com/user/GTOTechnology has created a few videos explaining how plugins work, but they are a bit lengthy, but are very good resources. HOWEVER the issue is that Bukkit has stepped away from the resources that he uses, so you cannot completely rely on it, but using both the link above that jefe mentioned, the vids, and looking at other plugins and their code, and know something about java, plugins are not really that bad