Respawn creatures droping items?

Ok, I was wondering how I would make it that creeps that respawn after dying the first time drop items. It's not that simple because some of the creatures in my map can drop multiple items and some have a chance of dropping rare item and a chance to drop nothing like...(example) I kill a dragon and it has a 20% chance of dropping a Sword of Ultimate Destructive Power (isnt that name so creative=P), but thats all it can drop so 1 out of 5 kills will drop that sword, and some creatures, (bosses) have low chances to drop multiple items...How would I do this, most likely using triggers? Thanks ^_^

Yeah, you need triggers something like this:
Event - Unit dies
Condition - Unit Type of dying unit equal to Dragon
Condition - (Random Integer between 1 and 100) less than or equal to 20
Action - Create Sword of Ultimate Destructive power at (position of (dying unit))

Thanks! Thats was a quick reply. I appreciate it very much! ^_^ ^_^ ^_^