var imgObjs = new Array();
var ii, jj, nn;

for(ii = 0; ii < imgNames.length; ii++)
  for(jj = 0; jj < imgStates.length; jj++){
    nn = imgNames[ii] + imgStates[jj];
    imgObjs[nn] = new Image();
    imgObjs[nn].src = imgPrefix + nn + imgSuffix;
  }

function swap(img, state){
  if(!document.images) return;
  document.images[img].src = imgObjs[img + state].src;
}