Popup window to appear on an event

Hi,

I am trying to make a popup window to appear in my web form when a threshold is exceeded I tried with this code, but this is activated on button click, not when some event like in my case occurs Also it uses AJAX Can anybody refer me please to an example which would help me how to make a custom popup window to appear when an event happens?

Here is the code for the popup I found

http://ajax.aspnetcdn.com/ajax/jquery.ui/1.8.9/themes/start/jquery-ui.css"
    rel="stylesheet" type="text/css" />

I solved this on this way

if(parseInt(mark[1].substring(0,2))>80)
                        {
                            //function () {
                                $("#dialog").dialog({
                                    // title: "jQuery Dialog Popup",
                                    buttons: {
                                        Close: function () {
                                            $(this).dialog('close');
                                        }
                                    }
                                });
                            //    return false;
                            //}
                        }
Does anybody have a better idea how to make a better customized popup?
Thanks