<form onsubmit="return check(this)">
发送日期：<input type="text" name="tempdate" value="2012-10-18" /> 
时：<select name="temphour">
<script type="text/javascript">
    for (var i = 0; i <= 23; i++) document.write('<option value="' + i + '">' + i + '</option>');
</script>
</select>
分<select name="tempminute">
<script type="text/javascript">
    for (var i = 0; i <= 59; i++) document.write('<option value="' + i + '">' + i + '</option>');
</script></select>
<input type="submit" value="开始发送" />
</form>
<script type="text/javascript">
    function check(f) {
        var now = new Date()
        , arr = f.tempdate.value.split('-')//时间格式我就不验证了，需要自己加
        , inputDate = new Date(parseInt(arr[0], 10), parseInt(arr[1], 10) - 1, parseInt(arr[2], 10), parseInt(f.temphour.value, 10), parseInt(f.tempminute.value));
        if (now >= inputDate) { alert('日历框中的日期必须大于等于服务器系统时间！'); return false; }
    }
</script>