I think it might be best to do a case page, that redirects to an attachment page or popup. This could be easily accomplished by doing a standard controller and one extension class. 

The page:

<apex:page standardController="Case" extensions="YourClassNameHere">
<script type="text/javascript" language="javascript" src="{!URLFOR($Resource.jQuery, '/js/jquery-1.5.1.min.js')}" ></script>
<script language="javascript" type="text/javascript">

//hides the main Case form and shows the attachment form on complete of the ticket save
function hideAfterClick(){
$('#mainCaseWrap').attr('style','display:none;');
$('#fileUploadWrap').removeAttr('style');
}

</script>
<div id="mainCaseWrap">
<apex:outputpanel id="mainCasePanel">
<apex:pageblock>

<!-- Put all case fields here that are required -->
<apex:pageBlocksection>
<apex:inputfield value="{!Case.SuppliedEmail}" />
<apex:inputfield value="{!Case.SuppliedName}" />
</apex:pageblocksection>

<apex:pageBlocksection>
<apex:inputfield value="{!Case.Subject}" />
<apex:inputfield value="{!Case.Description}" />
</apex:pageblocksection>
</apex:pageBlock>

<apex:commandButton id="submitCaseBottom" action="{!CreateCase}" value="Create" onComplete="hideAfterClick();"></apex:commandButton>

</apex:outputpanel>
</div>

<div id="fileUploadWrap" style="display:none;">
<apex:outputpanel id="FileUpload">

<apex:inputFile size="75" id="fileattachmentinput" value="{!bAttBody}" filename="{!sAttName}" contentType="{!sAttType}"/>

<apex:commandButton value="{!$Label.Save}" action="{!saveAttachment}"/>

</apex:outputpanel>
</div>
</apex:page>

 the controller:

public with sharing class YourClassNameHere{

private Final Case cse;
public string sCaseId{get;set;}
public string sAttName{get;set;}
public blob sAttBody{get;set;}
public string sAttType{get;set;}

public NewTicketCreationCon(ApexPages.StandardController stdController){
	this.cse = (Case)stdController.getRecord();
}

public pageReference CreateTicket(){

/*define the DMLOptions for the Case*/
database.DMLOptions dmo = new database.DMLOptions();
dmo.assignmentRuleHeader.useDefaultRule = useAssignmentRule;

Case c = new Case();
c.SuppliedEmail = cse.SuppliedEmail;
c.SuppliedName = cse.SuppliedName;
c.Subject = cse.Subject;
c.Description = cse.Description;

insert c;
//set the case id so we can use it later
sCaseId = c.id;

c.setOptions(dmo);
update c;

return null;
}

public PageReference saveAttachment(){
if(sCaseId != null && sCaseId.lenght() > 0)
{
Attachment att = new Attachment();
att.Name = sAttName;
att.IsPrivate = false;
att.ParentId = sCaseId;
att.Body = sAttBody;
att.ContentType = sAttType;

insert att;
}
return null;
}

}

None of this was tested, but it should work lol