images über id oder namen in Javascripten ansprechen

[snatch]

Okay, das habe ich probiert, aber es klappt nicht:

hier mein quellcode:

script:
nav06 = new Image();
nav06.src = "./images/navigation/links.gif";
navOver06 = new Image();
navOver06.src = "./images/navigation/links_over.gif";

function navChange(imgID, overObj) {

imgID = "navEl" + imgID;
  overSrc = "nav" + overObj;

alert(imgID);
  alert(overSrc);

window.document.getElementById(imgID).src = overSrc.src;

} // end function navChange

aufruf in html:
<a href="" onMouseOver="navChange('06','Over06')" onMouseOut="navChange('06','06')">
<img id="navEl01" src="./images/navigation/links.gif" />
</a>