Hi,
[quote]Does anyone know how to open a different image in that window depending on the value of the DNIS??[/quote]
Yes, I know 

. Some light programming in Java is required to do so. Please find the steps and code below.
1/ It is necessary to modify your custom.xml as we need id of the interaction to be passed to welcome.jsp
[code]     <javascript-onaddinteraction>
      <![CDATA[
                document.forms.welcomeForm.elements.interactionId.value = idInteraction;
                document.forms.welcomeForm.elements.userName.value = userName;
                document.forms.welcomeForm.submit();
            ]]>
     </javascript-onaddinteraction>
     <html-body>
            <![CDATA[
                <form name="welcomeForm" target="_blank" method="get"
                      action="custom/welcome.jsp">
                    <input type="hidden" name="userName"/>
                    <input type="hidden" name="interactionId"/>
                </form>
            ]]>
        </html-body>[/code]
2/ And now we can add some Java code into welcome.jsp that will get DNIS of the interaction
[code]<%@ page language="java" buffer="none" contentType="text/html; charset=utf-8" %>
<%@ page import="com.genesyslab.ail.AilLoader" %>
<%@ page import="com.genesyslab.ail.AilFactory" %>
<%@ page import="com.genesyslab.ail.Interaction" %>
<%@ page import="com.genesyslab.ail.Interaction.Type" %>
<%@ page import="com.genesyslab.ail.InteractionVoice" %>
<html>
    <head>
   <script type="text/javascript" language="JavaScript">
      window.onblur = function() {
      setTimeout('self.focus()',100);      
      }
      window.resizeTo(500,400);
      </script>
        <title>Branding Notification</title>
    </head>
    <body>
        <center><b>
            <font size="6" color="#000099">
<%
String DNIS = "";
String imageName = "";
Interaction interaction = null;
InteractionVoice voice = null;
String interactionId = (String)request.getParameter("interactionId");
AilFactory factory = AilLoader.getAilFactory();
try {
    interaction = factory.getInteraction(interactionId);	
	if (interaction != null) {
		if (interaction.getType() ==  Interaction.Type.PHONE_CALL) {
			voice = InteractionVoice)interaction;
			DNIS = voice.getDNIS();
		}
	}
} catch (Exception ex) {
}
voice = null
interaction = null
factory = null;
switch (DNIS) {
	case "12345": imageName = "12345.png"; break;
	case "67890": imageName = "67890.png"; break;
	default: imageName = "unknown.png"; break;
}
%>
		<img src="<%= imageName %>" alt=""/>
            </font>
        </b></center>
        <hr>   
    </body>
</html>[/code]
I haven't been able to test the code so some "polishing" might be needed...
R.