myImgOut  = new Image();          // 
myImgOut.src  = "img_10/img/return2_r1_c1.gif";   // 

myImgOver = new Image();          // 
myImgOver.src = "img_10/img/return1_r1_c1.gif";    // 

function myMouseOut(){                     // 
   document.myFormImg.src = myImgOut.src;  // 
}

function myMouseOver(){                    // 
   document.myFormImg.src = myImgOver.src; // 
}