Erzulie is one of the 4 BID Elemental Guardians that were released last year. To order one now you need to go through the CDS (Custom Doll System) to place the order. The CDS is open from the 1st through the 15th every month and you can make your choice of gender, mobility joint option and resin color. The CDS doesn't have lay-a-way, so all dolls there have to be paid in full at the time of purchase.
Here's the link to the BID custom order page http://www.iplehouse.net/shop/step1.php?number=2321
Btw, there has been a bit of speculation about whether the 2011 Elemental Guardians will be available next year, so you may want to consider purchasing before year's end to be on the safe side. I had an Erzulie Boy and Efreet Girl on my "some day" list, but I've moved them up so I don't miss out.
Hope that helps.