If you decide to fight the Lich anyway (but I'd never go against Six's advice [img]tongue.gif[/img] )
just use anti-undead weaponry.
+ Cast Sunray from Daystar (if you got it)
+ use the Mace of Disruption (if you got it
)
+ use Azuredge (if you got it
, can be purchased at the CC)
Do so before he gets his defensive spells up, or after you've dispelled them.