I am a naive user of jquery 1.4.2. For showing cool modal dialog box on my webpage I am using it. It flickers when I open the modal dialog and then it disappears :)
$("#AlertBox").dialog({resizable: false,modal: true,autoOpen: false, show: 'slide', position: 'center',width:405});
$("#AlertBox").css({ visibility: "visible", cursor: "pointer" });
$("#AlertBox").dialog("open");
Have you included properly all the required .js files and the .css files in the webpage? Which modal dialog box are you using?
Perhaps you have included an external javascript or css file which is not loading properly?
Make sure that you are using jquery-ui-1.8.custom.min.js with jquery-1.4.2.min.js. I have faced same problem today I refered following link --> http://forum.jquery.com/topic/common-problem-jquery-ui-and-jquery-1-4-x