Xmas event details...

[Vigilia]

From Dyire's guide as usual:

http://ffxi.killvoid.com/forums.php?m=posts&q=142687&d=0

Overview
The Starlight Celebration is back again, but it hasn't gone off without a hitch. There are roaming Twinkling Treants fighting against Nomad Moogles, fake Smile-Bringers, and of course all the shiny items and furnishings you can only obtain during a special seasonal event! Don't worry about items you may have missed from a previous year, as it is still possible to obtain last Starlight Celebration's special items.

Cities participating in the event
Windurst Woods
San d'Oria North
Bastok Market

Treant Event
There are Smile-Bringers in the three cities, standing near the fountain. On occasion, they will disappear and a Twinkling Treant NPC will appear, fighting along side a Nomad Moogle. Find the Twinkling Treant and emote "/cheer" to cheer it on! Only with enough cheers will it be able to survive the Nomad Moogle's attacks and walk its way to the fountain. If the Twinkling Treant fails to make it to the fountain and is successfully defeated by the Nomad Moogle, you will have to wait until the Smile-Bringer disappears again and the Twinkling Treant spawns again to try the event again. If the Treant does make it to the fountain, it will disappear and the Smile-Bringer will re-appear near the fountain. Talk to the Smile-Bringer once the Treant is defeated and the Smile-Bringer will mention an imposter Smile-Bringer handing out shady gifts. The fake Smile-Bringer is an npc that is normally in the zone, but is strangely wearing a Dream Hat for some odd reason. Find the fake Smile-Bringer, confront him/her, then return to the real Smile-Bringer for your reward.

Real Smile-Bringers Locations
Windurst Woods - Atagei-Portagei - (H-11)
San d'Oria North - Charmealaut - (J-9)
Bastok Market- Christina - (G-9)

Fake Smile-Bringers Possible Locations
Windurst Woods
[_][_][_]-Retto-Marutto - (H-12) - In the Bonecrafting guild
[_][_][_]-Quesse - (K-12) - In the Chocobo stables
[_][_][_]-Taraihi-Perunhi - (J-10) -
[_][_][_]-Millerovieunet - (J-12) - Just above the AH
San d'Oria North
[_][_][_]-Vichyek - (F-4) - Near the Woodworking guild
[_][_][_]-Pirvidiauce - (D-8) -
[_][_][_]-Tavourine - (E-4) - In the Royal Armoury
[_][_][_]-Justi - (G-8) - In the Furniture store
Bastok Market
[_][_][_]-Belizieg - (E-8) - Delivery Box NPC near the AH
[_][_][_]-Harmodios - (K-10) - In the Music store
[_][_][_]-Peritrage - (F-10) - Back of the Armor store
[_][_][_]-Olwyn - (E-11) - In the Item store

Possible Prizes
After getting the furnishing, any prize you get after completing the event again is random. Trading fireworks and gifts you get from the Smile-Bringer to children NPCs may improve your luck on getting the Dream Robe+1.
Furnishing depending on Nation
[_][_][_]-Dream stocking for Windurst
[_][_][_]-Dream platter for San d'Oria
[_][_][_]-Dream coffer for Bastok
Dream Robe
Dream Robe +1
10 Fireworks
Obtaining the Dream Hat +1
Place all 3 tree furnishings that you can purchase from the Merchant Moogle stand in your Mog House. Some time later, your moogle will give you a Special Present. Use this outside to obtain your Dream Hat +1!
Inter-Nation Warping
Inter-Nation warping is back again! Every Vana'diel day, you'll be able to recieve a Kiddie present from the Smile-Bringers. Trade that present to any child NPC to raise your festive fame. Make sure you have a Dream Hat on, however, else you won't be able to act as a Smile-Bringer! You can purchase a NQ Dream Hat from teh Merchant Moogle stands. Once you have enough festive fame, the Smile-Bringers will give you the option to be warped to any of the other 2 nations. Remember though, warping lowers your festive fame, so don't forget to refill it by trading that present a day!
Merchant Moogle Stands
These items can be purchased at the Merchant Moogle stands. They are located at:
Windurst Waters - (G-10)
San d'Oria North - (D-8)
Bastok Port - (L-8)

The items and prices are as follows:
[_][_][_]-Popstar (440G)
[_][_][_]-Brilliant Snow (252G)
[_][_][_]-Sparkling Hand (252G)
[_][_][_]-Air Rider (672G)
[_][_][_]-Cracker (231G)
[_][_][_]-Twinkle Shower (275G)
[_][_][_]-Little Comet (275G)
[_][_][_]-Dream Hat (10,000G)
[_][_][_]-San d'Orian Tree (10,000G)
[_][_][_]-Bastokan Tree (10,000G)
[_][_][_]-Windurstian Tree (10,000G)
[_][_][_]-Kadomatsu (10,000G)

Edit:

Above thread also has reports that placing the items in your mog house will make your moogle "find" additional rewards in them.