[Radek]

To Masteraleph: It depends on your level. I suspect the game that your Turn Undead level (i.e., your level in the case of clerics) must be greater than the level of the turned undead if you want to suceed in turning. The greater is the difference between your Turn Undead level and the monster level the higher is your chance to destroy the undead. Let us note that liches have level 20 - 26.
My experience. I like to play a party of three dual class characters so that my level is 25 or so when it comes to the final deal with Bodhi. My ranger/cleric can enter the lair, leave the rest of the party near the exit and stroll the lair with Turn Undead active. All vampires, wraiths and similar monsters get destroyed immediately. They have no chance. Bodhi seems to be protected from Turn Undead - I have never succeed in turning her. Also those warriors formed from a skull, shield and sword are immune to turning undead.