All the steps are covered here (
http://www.lucasforums.com/showthread.php?t=143991) and here (refer to Saber Tutorial.rtf) (
http://www.lucasforums.com/showthread.php?s=&threadid=143456).
Custom items use custom icons, based on their naming convention. For example, if your new crystal was w_sbrcrstl99 then the icon file for it would be iw_sbrcrstl_099.tga (which you would have to make). Just use an existing icon as a template - make any changes you like then save it out with the appropriate filename.
As far as hex editors go, there are a bunch of free ones. A Google search should turn up plenty. You can also use trial versions of editors like Hex Workshop, but you don't need anything that fancy to be honest.