[AndrewGSW]

Could that mean the elements haven't loaded yet?

Yes, as has been mentioned a couple of times . You need to run the code that attaches events (using getElementById) after the page has loaded. You could either move it into code that runs on the window-load event or move all your JS to the bottom of the page, just before the closing BODY tag.

You might use a slightly extended version of your dollar-function:

        var $ = function () {
            // Example: var els = $('obj1name',obj2,'obj2name');
            // Saves having to write 'document.getElementById' repeatedly,
            // but could also be useful for grouping elements.
            var elements = {}, argLen, i, element; 
            for (i = 0, argLen = arguments.length; i < argLen; i++) {
                element = arguments[i];
                if (typeof element === 'string')
                    element = document.getElementById(element);
                if (argLen === 1)
                    return element;
                elements.push(element);
            }
            return elements;
        };

It is no where near as comprehensive as jQuery's but slightly more flexible than your current version. You can supply it a string (an elements' id), an element-object reference, or several of these separated by commas.