I want to romance with Viconia but i see shes evil and was wondering can evil stay with good(I have a pretty much neutral party, but i do lots of good deeds) so i was wondering if she'll stay in my party with, say some Neutral and Good characters and a rep of say, 17?

Yar, I've heard of someone dating Vicki when he was NG. just don't let your rep go over 18 or she'll leave.

SPOILER:

DON'T put Keldorn and Viconia together in SoA, he'll kill her.

Actually, whenever I'm romancing her, Keldy leaves her alone because she's learning to trust.

All my guys have been good, and the V ic romance always works. You have to be VERY nice and understanding to her, so I don't see why a Good alignment would screw that up- it makes more sense, actually.

im ng with rep 19 and still have romance with viconia

Evil characters will only leave if your reputation is 19 or 20. With Viconia in your party you rep is always -2, so that she won't leave due to you having too high a reputation, as she is a romance option.

Possible SPOILER
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I've actually heard that if you're nice enough her alignment shifts from NE to NG, if anyone can confirm this.

I have never done it, but I have seen it happen, much like a certain other NPC's alignment change. Think it was because of ToB though.
You could always download the Happy Group mod if you wanted to take up your rep.

I think it's kinda cool having a dual-personality though. Do good deeds, save kid's pets etc, while sharing your megalomaniacal desires with Viconia. Mwahahaha!!!!!