World Event

Is there any way to make a custom World Event in MaNGOS? I know how to create characters, items and loot, I just need to know if there's a way for it to automatically start when something happens, or at least let itself go on without me manually spawning every NPC.

a moded quest?
or put npc where you want then save world?

I was wondering more about how I could make it so that the event will start at one point, and then when I set it to end all traces will disappear (quest givers, NPC's, etc).

For example, take the world event of Gates of Ahn'Qiraj. A player initiates it by hitting the gong with the Scepter of the Shifting Sands, and from there it goes until it's pre-determined end point.

How can I do this so that my event starts for the whole server once someone does the right thing? Furthormore, how would I make it stop at the point I want (IE all of the event-specific NPC's are dead).

Anyone?