I'll explain this in terms of theory instead of "do this"
Items have a "grade" column, this "grade" is how you assign the drops ( you should know this )
Boxes are items that behave like mobs...the "drop list" for boxes is in the itemcreate.ini file.
In the database, find a "box" and look at it's ReqVg column. The number in the ReqVg column is the Itemcreate_## in the itemcreate.ini
[ItemCreate_##]
Item# Droprate
## is the number in the boxes ReqVg column
All of this can be found in the how to setup Shaiya pserv pdf somewhere in the sticky area ;) Read through it. It's got a huge amount of good info in there all in one place.
Happy gaming