If you are running into issues trying to smooth bitmaps dymaically then try these things.

gskinner has a blog post on a small bug in the player where smoothing is set to false after the bitmap data gets changed.

var bmp:Bitmap = new Bitmap(null,true);
trace(bmp.smoothing); // true
bmp.bitmapData = bmpd;
trace(bmp.smoothing); // false

If that still hasn't solved your problem and you are still getting aliased bitmaps then setting the stage.quality property to StageQuality.BEST should do the trick.

stage.quality = StageQuality.BEST

For a good comparison of this check out this link: http://www.geocities.com/niquon/bitmap_test/