I don't really know how to make items myself beyond Blender I think. They use it to make items for maps and stuff and I'm pretty sure that's how items would be made. Could be wrong though. I really hope someone comes along that can help you a bit better than I did. xD
Edit: There is this one person I know that makes items I think. She has some items in the Legendary items that players can download. Her name is Tailgate. Pretty sure you can shoot her a message and ask her. Here is her profile. (http://www.feral-heart.com/index.php?option=com_jfusion&Itemid=2&jfile=index.php&action=profile&u=211585)
I recommended using blender as already suggested & looking at tutorials and things. Once you got a general idea and grasp on it, you visit this link here on to to make custom textures for your items.
Click Me ~! (http://www.feral-heart.com/index.php?option=com_jfusion&Itemid=2&jfile=index.php&topic=30544.0)
Good Luck Floof ^^