One "gotcha" to watch out for is to make sure that the item ID is less than 32768. I've read that the cilent doesn't like IDs that are 32768 or higher.
By not showing up, do you mean that you can't summon it, or that it isn't visible? If it simply isn't visible, make sure you have set the icon ID and visuals properties. Making items is kind of a black art. I've been screaming for a while that we need to write our own client so we have better control over the process
