Mordheim does have a human warband, and a vampire warband.
Only four of the core warbands were used. Human Treasure Hunters, Witch Hunters, Chaos Cultists and Vampire Counts. The four of them worked pretty much as described in the Mordheim rulebook. Setting wise we were more inspired by Robert E. Howard's Solomon Kane series, than the default Old World of GW. The Warbands were pretty much left untouched rules wise, the only major change was with the Chaos Cultists, and that was more theme than mechanics. The Cultists in this setting were Devil Worshipers, a circle of Dark Sorcerers who have bartered their souls away for power. Given than some of them get mutations, while only one of them get's sorcery, you can see the dark powers are fickle. The Possesed were just that, cultists that had become wholy demon ridden.
I forget what we did scenario wise. But I do remember a Town Cryer that had a two player scenario, where the warbands are exploring a series of Vampire infested catacoombs.
Clapham
You used Mordheim?
Could you explain more