I had trouble at first, but I successfully built a good Dual-Wielding Warrior.

Is your dual wielding warrior acting as your tank? If not, then just flush those points in 'em like he/she was a rogue. If he/she is... wtf are you doing using a duel wielder as a tank??? 
Also the Reaver specialisation goes very well with a duel wielding warrior, I might add.

Go dexterity so you can dodge rather than take hits

I just put all my points into Strength and Dexterity (some into Cunning and Willpower) and it worked out fine. I also used heavy armor and it worked.

I would have put most of those constitution points into dexterity because dexterity helps you evade attacks.

But it also depends on the type of dual-wielder you are, because swords and daggers benefit from different attributes.

" @Abyssfull:  I had a duel wielding dwarf as a tank. I could wade in and kill a whole bunch of dudes before Alistair could take a single swipe. My character could deal out twice the damage of any other character in the game, and I could do it while rarely dying. "

Focus on Dexterity and Strength.  Ideally you'll have another Warrior (preferably with a shield) with you to soak up most of the damage, in which case you don't need to worry about Constitution too much.

yeah, strength and dex. your gonna wanna play him/her as a rouge. The reaver class will def. help out too. on my second play through, when i played as a warrior, i preferred tanking over anything. But i imagine the dual wielding warrior works just like a dual wielding rouge. 

" yeah, strength and dex. your gonna wanna play him/her as a rouge. The reaver class will def. help out too. on my second play through, when i played as a warrior, i preferred tanking over anything. But i imagine the dual wielding warrior works just like a dual wielding rouge.  "

I don't know about point distribution, but you definately want to always be using the dual strike ability combined with a mage casting haste on you. You'll attack like lightning. If you have low dexterity though a lot of your attacks won't hit.

" @lordbazuco said:

" yeah, strength and dex. your gonna wanna play him/her as a rouge. The reaver class will def. help out too. on my second play through, when i played as a warrior, i preferred tanking over anything. But i imagine the dual wielding warrior works just like a dual wielding rouge.  "

Besides the Reaver specialisation, it is pretty pointless to have your warrior go with duel wielding weapons. You're going to want to have a rogue in your party anyway for the lockpicking, so might aswell have him/her take up the duel wielding duties since the class doesn't have much alternative anyway.  "

" Focus on Dexterity and Strength.  Ideally you'll have another Warrior (preferably with a shield) with you to soak up most of the damage, in which case you don't need to worry about Constitution too much. "

" @Abyssfull: I like the idea of a dual wielding Warrior. Duncan was a badass dual-wielding Warrior and I wanted to recreate that. "

I'm leveling a DW warrior at the moment as well, and The Character Build Handbook over at the official forums has proven quite insightful.
  http://social.bioware.com/forum/1/topic/96/index/515316/1

" I have a dual-wielding warrior (currently Level 11) and I was wondering if I should put the majority of my points into Constitution, to make up for not having a shield. Would it be a bad idea to wear heavy armor? Any other suggestions are welcome. "

I re-speced Sten to be my dual-wielding tank and it worked awesome, just focus on Dex and Str in that order, you´ll end up an awesome tank that can deal some serious dps too. Make sure you use the biggest armor you can find, and having the tanking ring from Orzammar doesn´t hurt either.