Vtank will use whichever caster you currently have equipped to cast vulns and then if a different caster is set for a type of critter it'll change before casting wars. It kinda sounds as if you don't use many specific creature spell setups and just 'Default' creature type for most mobs. If that's so you'll want to add more specific creature types, set your damage type and then your preferred caster for said creature type. I've found that Vtank is easier to manage if you create a number of different Profiles with a separate one for each hunting area, going thru a big list of mobs to change/adjust something is a pain otherwise.
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Edits are for spelling :^)
Trophy Compendium
http://vnboards.ign.com/message.asp?topic=90389010
/a Devil's Saint says, "what we teach our Children we become" June 3, 2008