This example does not use scrollRect:
http://img296.imageshack.us/my.php?image=tiles24yc.swf


The way it works:
*there is tileset image in the library (1 gif with all tiles on it)
*random tiles are then chosen from there and drawn on myBmp bitmapData
*myBmp is 640x640 px
*tiles mc is created
*another bitmap (bm1) with exact size of stage is created
*at each frame bm1 is update from bigger myBmp using copyPixels
*bitmap (bm1) is drawn into tiles.bmp mc

No mc is ever moved here, only thing that changes is bm1 which is updated using copyPixels.
/*originally posted by tonypa, moved to its own thread by tomsamson*/