Thumbnail to larger pic display

Hello there,

I am in desperate need of some assistance (again). I have created some thumbnail images (as buttons) that need to open to larger images once clicked.

Currently I have it set up to open a new browser window but this is not what I want.

Herewith existing code:
[SIZE=1][COLOR=royalblue]thumb1.addEventListener( MouseEvent.CLICK, goto_thumb1 );[/COLOR][/SIZE]
[SIZE=1][COLOR=royalblue]function goto_thumb1(e:MouseEvent):void
{
navigateToURL( new URLRequest( “thumb1.swf” ), “_blank” );
}[/COLOR][/SIZE]

I need the larger pic display to be restrained to the size 600x400 and preferably to load in front to the main website (like a popup).

I would appreciate your URGENT assistance.

Many thanks in advance.
Lisa