>Is it possible to make a Warrior character that can eventually
>cast spells...?

This spec isn't possible, although Templar is an anti-magic Warrior class.

>
>Or a mage character that can be effective and not get
>annihilated in the thick of battle...? Is the Arcane Warrior
>specialization I saw going down that route?
>
>I hope so...

I'm not sure if I'll go down this path myself, but I've heard that AW is actually a pretty strong option for a mage.

Here are a list of the classes and their skills:

http://dragonage.wikia.com/wiki/Category:Classes