Ok, if you already have an AmebaID, go to http://pigg.ameba.jp. Then login with your AmebaID. From there it's easy to create your pigg.
Note: you can change face parts afterwards, but you have to pay 30 AME.
However, you get 5 free tickets to buy stuff with when you take the tour!!
Now you're done! :D
Go here to learn about your room