Phil,

 

Please try the following code:

 

var img=document.createElement("IMG");

var editor=document.getElementById('<%=Editor1.ClientID%>'); 

var editdoc = editor1.GetDocument();

 

var newwin_1=showModalDialog("CuteSoft_Client/CuteEditor/Dialogs/InsertGallery.aspx?settinghash=<%=Editor1.Setting.GetHashString()%>", {img:img,editor:editor,editdoc:vars.editdoc}, "dialogWidth:670px;dialogHeight:650px");

 

Hope it helps.