Are they? I am starting fresh and am going to role a Paladin type of character. I want to use Dawn Breaker and Spell Breaker but if they're leveled, what level are they at their best? If not, anyone know what level you need to be do get those quests? I got them both on my original character but he was pretty high leveled and I had done smithing and enchanting so we was basically indestructible.

All your questions are answered here;
http://www.uesp.net/wiki/Skyrim:Artifacts

If its not listed just search the site for the specifics of that weapon.

Thank you. Good to know it IS leveled and I'll be kicking myself if I get them early on.

I think you misunderstood the list

Dawnbreaker and Spellbreaker isn't leveled.
The leveled artifact/unique weapons are: Chillrend, Nightingale Blade + Bow, Dragonbane and the Gauldur Sword + Bow.
The leveled armor & shields are: Nightingale set and Shield of Solitude (which you'll want to disenchant anyway).

I'm just reading that wiki article, and the article seems to be saying vast majority of artifacts are not leveled and a few items are leveled and capped at level 46. And all those leveled items (Chilrend, Nightingale Bow, Nightingale Blade) are associated with the Thieves Guild quest. Am I interpreting it correctly?

Ah. Found another list. http://www.uesp.net/wiki/Skyrim:Leveled_Items These items are much less exciting.

Yep, it's mostly items from the TG quests. I guess Dragonbane is the only notable leveled item otherwise ^^