Vitamin D Question? Please Help - The difference in different types of vitamin D (Jun/18/2009 )

Hi All,
Im a newbie to the forum and was hoping that someone would be able to help me with this never ending quest of mine in relation to vitamin D. I have ordered in choleciferol (What i thought was vitamin D) and have since discovered that it is actually a vitamin D precursor. Does anyone have any knowledge of vitamin D and its in vitro functions. I am looking for info on the different types and where is the cheapest place to source them?

Any help would be greatly appreciated

this wikipedia page has a good explanation (and structures):

vitamin d