[thelist] JavaScript rollover problem in IE4,5

http://roselli.org/adrian/temp/rollover.asp

since my gallery is getting so big, and since i want to keep image
load down, i'm trying to break out my arrows into one re-usable
rollover, and over and over...

works fine in NN3,4...

in IE4,5:
'document[...]' is not an object

offending code (watch for wrap):

<SCRIPT LANGUAGE = "JavaScript">

<!--

if (document.images) {

        on = new Image();
        on.src = "b_arrow_on.gif";

        off = new Image();
        off.src = "b_arrow_off.gif";
}

function rotate(state,imageName) {
        if (document.images) {
                document[imageName].src = eval(state + ".src");
        }
}

// -->

</SCRIPT>