I have looked around and couldn't find info on this.

I know if you dual wield the same spell and cast both it makes a big spell. If you dual wield 2 dif spells and cast them does it do something unique like Fable 3 or Magicka, or can you only cast 1 at a time. Although if it is only 1 at a time I'm sure there will be a mod for this.

http://twitter.com/#!/DCDeacon
check his tweet saying, "No, not possible."

No you can't combine 2 different spells. It was going to be an option but Bethesda mentioned at some point (don't remember when though) it was to comlicated to get to work well so it was removed.

You can duel wield 2 spells at the same time. In the demo you see Todd using Detect Life and Frenzy to kill 2 bandits. You just can't combine those 2 spells at the same though to create a super spell

The spells won't combine, but you can use them at the same time.

And it was mentioned that a journalist demoed the game and used both a fire spell and a lightning spell at the same time.

Indeed. Some players at the eurogamers convention said wielding flamethrower and shock-thrower (... chain lightning? i forget) at the same time was just as awesome.