IF I am not wrong they get a holy symbol after 25lvl. Well Viconia get the symbol in one of my games, but didn't in other. Why?
Oh, something else: have you seen "Turned paladin" message when turning undead with Viconia?

1. Maybe it's because she changed alignment? If she does before lev25, she doesnt get a symbol, if she does after; she cant use her evil symbol.

2. Yes that happens, Evil Clerics can Turn Undead, Control Undead (if they are high enough level, this happens after turning), and Turn Paladins.

Evil clerics can only turn paladins in ToB btw.

Viconia changes alignment? I really should take her along for the ride one of these days.

No, she can change alignment. For that too happen you have to talk the right way to her. (Simply stay away from all lines that are from the dark side, say how you hate all the violence and stuff.) You, know I'm getting more and more convinced, that all these drow are simply tough layer on the outside, softhearted on the inside :p

Her alignment is <u>NOT</u> changed, but she didn't get the symbol.