A lot of websites suffer from the problem that the
flashplayer sometimes reports lower values for getBytesLoaded,
though the movie IS completely loaded.

I suggest to use something like
this.getBytesTotal() - this.getBytesLoaded() < 10
or a similar value, most likely the difference is
just 1, if any (<- classic index error)

just my 2 cents

ok....fair point :)
this is probably better

MovieClip.prototype.isLoaded = function (){ return (((this.getBytesLoaded()/100)*this.getBytesTotal())>99); }