[edit] Short version = what Karpov said a minute ago
You can only add items and access then through the console command above. How to combine the inventory and 3D is rather a good question, but the only one who knows something about it is Karpov. Maybe Luther knows something about it, I'm not sure though.
The bits I mentioned here :
http://fodev.net/forum/index.php/topic,26833.msg231777.html#msg231777 should resolve that. Karpov sorted it out at some point in the past and has covered it in more detail, but as the 3d repo only covers the client folder, it's not included in the 3d svn thing.
The bits that need to link together are values in client_main.fos (in server/scripts), which should correspond to the objects in the fo3d file. If you need them, you should be able to get item names and numbers from itemnames.lst in Server/data, or from looking at the proto files in server/proto/items, but for now it will function by simply linking the numbers as in the file below.
Anyway the client_main.fos should be uploaded here
http://www.sendspace.com/file/nxevzl, which you can drop in your own server/scripts folder and it should work on a basic level.
Note that only the pre-existing weapons/items will work in an "equip object in game>model appears in 3d" sort of way. Anything we've added ourselves (i.e. extra armours, weapons etc) would need adding as items first (with floor icon, inventory icon, short description, long description, stats and values etc).
If you've been looking at different things with ~param 0 151 x, then you'll need to set it to ~param 0 151 -1 to return to the "use linked models" sort of mode.
[edit2] Karpov says above it should be 0 instead of -1, so try that first (~param 0 151 0).