In my first run through SOU with a Neutral Good half-elven cleric, I met Tymoferrar first and was so dazzled by his charisma, that I accepted his quest. Upon meeting J'Nah however, I also accepted her quest. Then without the Gnolls assistance, I summoned a dire boar, buffed myself and Dorna up with bless, prayer, divine power, darkfire, cats grace, barkskin, then scoffed a potion of speed before using the powder from distance. I then ran headlong into the fray by targeting J'Nah first of all and quickly she fell, having cast very minimal spells thankfully.
Going back to the White Dragon, I thought I would roleplay it with a sly kind of humility by accepting his reward and letting him live. However, downright avaricious delusions of grandeur and thoughts of what it would be like to be a frost giant filled my cleric's usually reasonably virtuous mind. Needless to say, I turned on him, used the phylactery and destroyed him much more easily than I thought possible.
Oh the shame my cleric felt after the deed was done!!
Mind you, the dragons in NWN generally are fairly pitiful I think compared to the beauteous Wyrms found in Baldur's Gate II. I've never really had any problems with any of them in NWN - even if I haven't played Hordes yet! (Shall start it soon...if I can get over the fact that you can't start at level one...)