Attachmovie - removing one MC and loading another

Hi I need a little help with this please:

On the root of my movie I have a empty container MC called ‘container’.

I have a number of MC’s that will load into this container via individual buttons…lets say ‘but1’ loads ‘MC1’ into ‘container’, ‘but2’ loads ‘MC2’, ‘but3’ loads ‘MC3’ etc.

Each of these MC’s is animated in two halves…an ‘intro’ which plays when the MC loads and then it stops midway.
The last half is an ‘outro’ for smooth transition when it unloads before the next MC loads.

What I need to know is how to:

a) write the correct syntax actionscript on each button that basically says:
on release, play the ‘outro’ of the current MC and once this has happened, attach the relevant MC and play.

b) as the buttons (which load the MC’s) can be pressed in any order, I can’t state the actual name of the existing MC to play the ‘outro’ of, so it needs to play the current/existing MC’s label ‘outro’…whichever is there.

c) it needs to know when it has reached the end of the currrent MC’s ‘outro’ before it loads the new MC

(NOTE: I am NOT attaching external swf’s as my movieclips…all movieclips are in the library of my one, main flash movie)

Hope I have written that clearly enough for someone to understand

Thanks in advance

Chris W