function newImage( imgSrc ){

 var imgName = new Image();
 imgName.src = imgSrc;

 return imgName;

}

function change( imgName, imgLocation )
{
 document[imgName].src = imgLocation ;
}

if (document.images)
 {

 dallas_over = newImage("images/Dallas.jpg");
 collin_over = newImage("images/Collin.jpg");
 tarrant_over = newImage("images/Tarrant.jpg");
 grayson_over = newImage("images/Grayson.jpg");
 denton_over = newImage("images/Denton.jpg");
 }