About dot stacking from different casters of the same class (as much as I hate to post it):
from here:
http://everquest.allakhazam.com/hist...es-2002-2.html
Damage Over Time (DoT) spells are spells that linger on the target
doing damage. Until today two different characters could not have the
same DoT spell on the same target. As long as one copy of the spell was
active any new version of the spell would not take hold. After today
the same DoT spell cast by different casters can affect the same target
at the same time. Also, if you cast a DoT spell on a target and you
already have that spell active on it, the spell will refresh. (Note: It
will not be possible to stack Lifeburn).
This does not allow for inferior spells to stack along with superior
spells. (Example: Two Necromancers can both land Boil Blood on the same
target. However, Heat Blood, being an inferior spell, will still not
stack.)
Several DoT spells that have debuff components such as Tuyen's Chant of
Frost and Breath of Ro will not stack due to the balance issues of
having several hundred points of Resistance debuffs on a single NPC.