wel.. makeing Items is rather a tricky business... I don't think many tutorials would be out yet- since it's a new feature, but if i see something, I'll post a link.
If you just want to convert other things into items, like what I done (mostly) on my thread, they you'll need a converter since most models are in .OBJ files, when you need .Mesh files. something like AC3D would be good, but you need a mesh plug-in.
if you want to make models; then you'll need something like Blender.
to get them ingame. you need the mesh file, material file and png file. drag all of them to 'items' (folder in FH). then, there is a material file called 'Items' you can add items that way. just type it the right code. (or copy and paste the whole of the santa hat, but chenage the mesh) and test it in-game...
sorry if it's confuseing or not explained well :/ I'm not good at explaining...