Rules for using the Legio Custodes and Sisters of Silence miniatures included with Burning of Prospero in games of Warhammer 40,000 are up on the GW site. Since "Age of Darkness" is an expansion for 40k, we are pretty sure it's cool to use these 'till we get our hands on the new White Dwarf (or a list made by Forgeworld).
You can download them here:
What do you think about them? Also, have you seen what's lurking behind these Custodes?^^