How can I stop my character from turning when moving it forward?

when moving forward my character slowly turns to the left or right which is not good. i'm using the third person controller/anim from the unity platform tutorial with my own model if that helps, anyone have a clue to why this could be happening? still trying a few things out but thought i'd try a post to save precious time. thanks chaps

classic, had the cam targeted at the head controller! that'll learn me to speed build, the mesh was the choice below it so i'd accidently clicked the wrong one :)