Content-Dispostion Attachment Problem

[rbmanian]

In an aspx page on a button click event(post back) i have the following code.
byte[] baResult = ProcessReport()
Response.ClearContent();
Response.ClearHeaders();
Response.ContentType = "text/html";
Response.AddHeader( "Content-Disposition", "attachment;filename=report.html");
Response.AddHeader("Content-Length", baResult.Length.ToString());
Response.BinaryWrite(baResult);
Response.Flush();
Response.End();
The client is displayed with download dialog box and when the user clicks
the open window the page is opened in the same IE window and it is not
opening in a different IE windows. Is there a was to force it to open in a
new IE Window.
When it is not a html content and if it is text, external application is
opened. Why a second IE is not opened when the attachment is of type html.
Regards
Balu