Other methods include creating bitmaps of the two movieclips, silhouetting them into a colour (say, red) and then overlaying them using a blend mode like multiply and then checking to see if the bitmap has any of the colour that should be generated when the colour is multiplied (ie red * red). There is a good function that uses this available on the internet.
@Faceless: That seems to do the job too, but the code in the post (no idea about the one attached, wasn’t able to download it without an account) only worked with top-left registered MCs, and would need a little tweaking to get it to work with centrally registered/otherwise
Yes, you can do bitmap pixel collision testing, but it is often more expensive than other methods. Pixel-pixel collision checking should only come when fine detail is needed and only after generic collision checking methods have determined that a collision is likely.