How to do combined animation

I want to combine 2 animation, walk forward and walk side, so when i press both forward and side key, the character would move in an 45 degree angle from the 2 basic directions.
Is there any example or even is that posible?

Check out Rune Johansen’s Locomotion at
http://runevision.com/blog/2008/07/locomotion-system-overview.html