CS5 Explode Animation

Hi there

I have a boulder/rock image that I have turned in to a MovieClip.

What I want to do is, have it explode (upon impact with a bullet) so I need to make an explosion animation within the timeline.

I have tried doing ‘break apart’ and then cutting bits away and using a shape tween but it looks awful.

What would be the best way to achieve an explode animation with the boulder MovieClip (which is simply this PNG converted to a MovieClip http://www.gemixin.co.uk/images/Boulder.png) within Flash CS5?

Also on the same subject, I have the boulder doing a simple rotation animation at the moment (looping from frames 1-25), but would there be a way of adding the explode animation on later frames (maybe frame 50 onwards) so that it doesn’t play initially, but only plays when called. For example I can call gotoAndPlay(50) when a bullet hits the boulder, but how can I get it to play only frames 1-25 in the first place and ignore frame 26 onwards until told otherwise?

Hope that made sense!

Any help appreciated.

Thanks
Gemma