One of the problems with D'Jinni - at least as of 1.4.5 which is what we have now - is that there is actually no way of adding a cutscene placeable. The placeables which were in your area at the time you created the cutscene are available within the cutscene, but the 'Select new CutscenePlaceable file' widget does not work.
So, if you want to use a weapon (or any other prop) in a cutscene, you must place it somewhere handy in your area before you create the cutscene file. But wait - what happens if you forgot?
Well, it turns out there's a way.
Subverting an existing placeable[]
In the cutscene editor, 'Cutscene Objects' pane, expand the 'CutscenePlaceable' branch. Choose a placeable which is never on camera in your cutscene (or whose absence won't be missed). Right click on it in the 'Cutscene Objects' pane and choose 'Change template'. You can now change its template to any binary model (MDB) you actually have included in your module. So, include the model for the object you want into the module, and you'll be able to make it into a cutscene object. When you do this, Djinni prompts you to ask whether you also want to change the object's name (it's probably a good idea to do this).
Now select your newly remodelled and renamed object. In the timeline pane, you'll see you now have a different set of properties from those you have when you select a character or a camera. The interesting ones are 'parent' and 'hookpoint'.
Parent[]
The 'parent' of the placeable is the object which it is to be attached to. If someone is to carry or wield a sword, the 'parent' is that character.
Hookpoint[]
The 'hookpoint' is where the placeable attaches to the parent. Different parent models have different hookpoints. If you want the character to carry the sword on his belt, select the hookpoint 'swd_s'. If you want him to carry it on his back, choose 'swd_l' or 'swd_r'. If you want him to weild it, choose 'rhand'.
Of course you can change the hookpoint during the cutscene, simply by placing an action on the 'hookpoint' line of the timeline, and specifying the new hookpoint. You need to time this to coincide with the right point in the characters 'drwswds' action, to make it look convincing.