tb1d = new Image();
tb1d.src = "/images/text_links/textbutton_dark2_1_0.png";
tb1b = new Image();
tb1b.src = "/images/text_links/textbutton_light_1_0.png";
tb2d = new Image();
tb2d.src = "/images/text_links/textbutton_dark2_2_0.png";
tb2b = new Image();
tb2b.src = "/images/text_links/textbutton_light_2_0.png";
tb3d = new Image();
tb3d.src = "/images/text_links/textbutton_dark2_3_0.png";
tb3b = new Image();
tb3b.src = "/images/text_links/textbutton_light_3_0.png";
tb4d = new Image();
tb4d.src = "/images/text_links/textbutton_dark2_4_0.png";
tb4b = new Image();
tb4b.src = "/images/text_links/textbutton_light_4_0.png";
tb5d = new Image();
tb5d.src = "/images/text_links/textbutton_dark2_5_0.png";
tb5b = new Image();
tb5b.src = "/images/text_links/textbutton_light_5_0.png";

<!-- repeat the 4 lines above for any subsequent images. -->

function swap(){
if (document.images){
for (var x=0;
x<swap.arguments.length;
x+=2) {
document[swap.arguments[x]].src = eval(swap.arguments[x+1] + ".src");
}
}
}