JavaScript Fade Function Not Working

var i = 0;
var max = 100;

function showMenu() {
for(i = 0; i < max; i++) {
setTimeout("document.getElementById('contextlinks').getElementsByTagName('UL')[0].style.filter = 'alpha(opacity="+i+")'",100);
} }

This is supposed to increment the alpha opacity of the UL inside the DIV contextlinks by 1% every 0.1 seconds (for a fade effect). However when the function is activated, the opacity is set directly to 100% rather than increasing bit by bit.