Hittest?

hello again…big problem again

Ive got a code to move a MC on the main stage together with the mouse, in the the X axis, … difficult to explain. But now the client wants that this MC movement works only when the Y position of the mouse is over the 300 px . I thought I need a hit test or something elese. Please help. Here is the whole code.

function moverPanel(cualClip, numeroBase) {
if (_root[cualClip]._x>_root._xmouse) {
diferencia = _root[cualClip]._x-_root._xmouse;
numDeslizar = diferencia/numeroBase;
_root[cualClip]._x = _root[cualClip]._x-numDeslizar;
//_root[cualClip]._alpha = numDeslizar;
}
if (_root[cualClip]._x<_root._xmouse) {
diferencia = _root._xmouse-_root[cualClip]._x;
numDeslizar = diferencia/numeroBase;
_root[cualClip]._x = _root[cualClip]._x+numDeslizar;
//_root[cualClip]._alpha = numDeslizar;

}
}

Gracias