Mouse listener and _xmouse problem

programming flash
1

Im having a problem. Im trying to use the onMouseMove listener to detect when my _xmouse passes 850px to scroll the nav onto the stage. The problem im running into is kinda obvious. When the _xmouse passes 850px it keeps running the action over and over,everytime i move the mouse. I tried different conditions but it keeps scrolling out.

Heres what i have so far:

ActionScript Code:
[FONT=Courier New][LEFT][COLOR=#000000]**var**[/COLOR] mouseListener:[COLOR=#0000FF]Object[/COLOR] = [COLOR=#000000]**new**[/COLOR] [COLOR=#0000FF]Object[/COLOR][COLOR=#000000]([/COLOR][COLOR=#000000])[/COLOR];
  mouseListener.[COLOR=#0000FF]onMouseMove[/COLOR] = [COLOR=#000000]**function**[/COLOR][COLOR=#000000]([/COLOR][COLOR=#000000])[/COLOR] [COLOR=#000000]{[/COLOR]
      [COLOR=#0000FF]if[/COLOR][COLOR=#000000]([/COLOR][COLOR=#0000FF]_root[/COLOR].[COLOR=#0000FF]_xmouse[/COLOR] >= [COLOR=#000080]850[/COLOR][COLOR=#000000])[/COLOR][COLOR=#000000]{[/COLOR]
          showNav[COLOR=#000000]([/COLOR][COLOR=#000000])[/COLOR];
      [COLOR=#000000]}[/COLOR]
  [COLOR=#000000]}[/COLOR];
  [COLOR=#0000FF]Mouse[/COLOR].[COLOR=#0000FF]addListener[/COLOR][COLOR=#000000]([/COLOR]mouseListener[COLOR=#000000])[/COLOR];

[/LEFT]
[/FONT]

I cant figure out how to get it to scroll out only once, when the _xmouse passes 850px. Any help would be greatly appreciated.

Jason.