In the unlikely event they actually collide, they would most probably pass through each other, tearing themselves apart in the process. More likely, one would be 'captured' by the more massive one, and they would start to orbit each other, one of them potentially 'eating the other'.
The odds aren't very high however
More likely still is that one will have its motion/path changed by the gravitational effect of the other.
There's some really good simulations around... it's pretty cool stuff
Jay