Like bykov already said...
Okay, bykov said basically what I wanted to say already but he didn't provide you any help, only critisism...
So, here's what I'm gonna add on.
1) Delete all the movieclips after the alpha has reached 0 or else it'll lag.
2) Learn to draw movieclips from scratch using only actionscript, check the "Cursors For The Future" that I made, all coded by AS and uses duplicating "particle system." If you don't know how, check up beginFill, endFill, lineTo, lineStyle in the ActionScript Dictionary.
3) Make it so that the AS code is dynamically inputted into each movieclip. Instead of having a movieclip already made and duplicating it or having a pre-written code and stamping it into each movieclip, make it so that each code is affected by some global variable. For example, make the rotation go up by globalSpeed and make globalSpeed go up every frame.
Last, I would like to say that the current Flash MX 2004 DOES NOT SUPPORT a "particle system." You still cannot make 10,000s of them. Perhaps you can make 100 or 1000 of them, but once you make too many, the FPS will go down. However, AS3 DOES have support for it and the amount of movieclips it can handle far surpasses AS2. It probably reaches its limits at 1,000,000 movieclips.