Reactors and Explode Modifier in 2.46?

I’ve been trying to get a mesh to explode after a collision with a particle in Blender 2.46. A good example is the bullet firing through a sphere tutorial here: Using 2.46 I can get the sphere to explode as an emitter or ‘spontaneously’ as a reactor by setting start and end values. But I can’t get it to explode in response to impact by the bullet target: ie the ‘collision’ bit doesn’t seem to be happening. As in the tutorial, the bullet is a single particle fired at the sphere from a plane emitter. All advice would be very welcome.

Apologies - posted this in Artwork not Support by mistake! Will repost there.