Works in Firefox & Opera, but not in IE8

Answer 1

Try not using innerHTML. IE historically does not allow you to innerHTML everywhere you would think possible. Instead try slower, clunkier DOM methods .appendChild(). For example, have the PHP return JSON or XML with the value/text pairs you need, then when you AJAX it do something like this:

PHP output (aka your http.responseText):

{value:"20100608",text:"date 1"},
{value:"20100609",text:"date 2"},
{value:"20100610",text:"date 3"},
{value:"20100611",text:"date 4"},
{value:"20100612",text:"date 5"}

JavaScript:

http.onreadystatechange = function(){
    if(http.readyState == 4){
        eval("var data = [" + http.responseText + "]");
        for(var i=0;i<data.length;i++)
            var t = document.createElement("option");
            t.value = data[i].value;
            t.innerHTML = data[i].text;
            document.getElementById("entry_7").appendChild(t);
        }
    }
}

I am not sure why you are experiencing the problem you are, but I am guessing it has to do with the innerHTML of a select element in IE. Try my above method and I'm pretty sure it'll work.

I hope this helps in some way.