If you dont already have seen,the tuts here are always a good thing to start with
social.bioware.com/project/527/theres also an explanation on how to add items to the player from start somewhere
But for example:
Go to file->new->placable,Then first,set the appearence to "Weapon Rack 2 (Container)"
From here,you have two pssibilities:
1.set the treasure categorie,then the game will randomly generate the items inside the container
2.A bit more down,under Stats,there is an option "inventory list",here you can add specific items from a list to the container
Save,put it to your area from the palette and go have some fun with your new weapon

. hope this helped a bit,its late and my english isnt that good anymore