[kh99]

OK, I haven't tried it at all, but maybe try this code instead of what you originally posted:

<script type="text/javascript">

function contains(a, ele) {
    for (var i = 0; i < a.length; i++) {
        if (a[i] == ele) {
            return true;
        }
    }
    return false;
};

function remove(a, ele) {
    var arr = new Array();
    var count = 0;
    for (var i = 0; i < a.length; i++) {
        if (a[i] != ele) {
            arr[count] = a[i];
            count++;
        }
    }
    return arr;
};

window.onload = function () {
        var taglist = document.getElementById('tags');
	taglist.value = taglist.value.replace (/\s+/g,'');  // strip space
        var tags = taglist.value.split(',');
        
        var populartags = document.getElementById('popularTags').getElementsByTagName('span');
        
        for (var i = 0; i < populartags.length; i++) {
            if (contains(tags, populartags[i].innerHTML)) {
                populartags[i].className = 'selected';
            }
        }
}

function doTag(ele) {
    var thisTag = ele.innerHTML;
    var taglist = document.getElementById('tags');
    var tags = taglist.value.split(',');
 
    // If tag is already listed, remove it
    if (contains(tags, thisTag)) {
        tags = remove(tags, thisTag);
        ele.className = 'unselected';
        
    // Otherwise add it
    } else {
        tags.splice(tags.length-1, 0, thisTag);
        ele.className = 'selected';
    }
    
    taglist.value = tags.join(',');
    document.getElementById('tags').focus();
}
</script>