The Head Start Event is coming for those who pre-ordered Guild Wars Factions. Your pre-order key will be good from 12:01 a.m. PDT (7:01 GMT) on Thursday, April 27th through 11:59 p.m. on Friday, April 28th (6:59 GMT on April 29th). This will give any new Factions characters and any "Ascended" Prophecies characters access to Cantha during that period. Further, you will have access to two extra slots (i.e. total of 6) if you already own Guild Wars Prophecies and choose to link the Factions key to your existing account.
And, perhaps most importantly, there is a 10 day grace period during which your new characters and Factions content will be retained (although inaccessible after the Head Start Event). You must enter a valid, full-access Factions key during that time or you risk having those characters and items deleted from your account. See the news article "Character Slots for Head Start Event 24 April 2006" for details.
Hopefully the Xunlai agents will be available. I'm so new to this I'm really not sure if "Ascended" is the same as "Seared" but I think it must be. So, my new Prophecies characters won't be ready. I'll have to make a new Assassin
Apparently there will be some Naga Fangs you can collect by killing the invading Naga, and you can trade them in for Tengu Masks at Shing Jea Monastery, but only during the Head Start Event. Whee!!!
Where can you get access to the Guild Wars Factions Head Start Event? You have to buy the Guild Wars Factions Pre-Order Gift Pack. It is in stores now, I've seen it in area stores. I bought mine from online, though.