Of course, it would refresh the page. It's server-side handle that would require this to produce any changes on a remote client. However, don't forget ASP.NET controls also have a Client-side Object Model(CSOM) in JavaScript (which you can use to handle events and manipulate the control). I think what you need is this sample about Dialog Window Client Events and note in there you have the very same functionality (show button) ready for the Show Dialog image button in WebDialogFrame.aspx:
<img id="ShowDialogButton" src="<%= this.GetGlobalResourceObject("WebDialogWindow","ClientSideEvents_ShowDialogImage") %>" width="98"
height="24" alt="<%= this.GetGlobalResourceObject("WebDialogWindow","Client_Side_Events_Tooltip_1") %>" onclick="$find('<%=WebDialogWindow1.ClientID%>').set_windowState($IG.DialogWindowState.Normal);" />
I have taken out the important bit you can assign as click handler to whatever you see fit on the client-side and added explanations:
// Show the dialog
function showDialog() {
// get reference to the Infragistics.Web.UI.WebDialogWindow instance
var dialog = $find('<%=WebDialogWindow1.ClientID%>');
//perform any checks neccesary or skip them, it's ok to
//set Normal state even if the dialog is already visible
if (dialog.get_windowState() != $IG.DialogWindowState.Normal)
//set state to Normal
dialog.set_windowState($IG.DialogWindowState.Normal);
}