What script do I need to write to have some one flourish their weopn in a dialog.

You don't need to write any new scripts. There is an existing script named a_flourish that you can use. Just add the NPC's tag you want to perform the flourish as a string parameter.

EDIT: Oops. I just noticed that you were talking of K1. In that case copy/paste the TSL script and replace the string parameter with the NPC's tag.
void main() {
object oNPC = GetObjectByTag("NPC_tag");
CreatureFlourishWeapon(oNPC);
}

Thanks. I wasn't sure what to do for it.

That function does not exist in K1.

Hmm, I guess you're right. Then I don't think you can flourish weapons in dialogue. The closest thing is to use the dialogue animation ready. That way the characters should raise their weapons without flourishing them and drop into a fighting stance.

Hmm, I guess you're right. Then I don't think you can flourish weapons in dialogue.

You could probably do a script that checks the base item type of the equipped weapon and then use PlayAnimation() to make the NPC play the appropriate flourish animation for that type of weapon. That wouldn't work for modded weapons from other people's mods that use custom base item types though.

Hmm, I guess you're right. Then I don't think you can flourish weapons in dialogue. The closest thing is to use the dialogue animation ready. That way the characters should raise their weapons without flourishing them and drop into a fighting stance.
I had this problem with K1. But I managed to get around it.

When I wanted to flourish a weapon during dialogue in K1, I wrote a script that would unequip then reequip the weapon in question. Because when you equip a weapon it automatically flourishes. It might not be the simplest of methods, but it works. :P