How to limit the movieclip's movement area

Hello, friends. I have two movie clips. one is smaller and supposed to be moved within the larger one. And the movement is controled by four buttons for up,down, left and right on the flashpage. Does any one have idea how to make it? Thanks a lot in advance!

give the smaller mc an instance name, and then set the boundaries of the mc, like,

//define boundaries for small mc
minX = 100;
maxX = 300;
minY = 250;
maxY = 450;

//script your control buttons to move the small mc.
..
..
..


//when the small mc have reaches the far right
if (smallmc._x > maxX){
smallmc._x = maxX;
)


.... and so forth.

Thanks a lot!