HOTFIX: IE7 does not open a link in a new window as expected after you use Dynamic Data Exchange to integrate a program into IE7
Consider the following scenario. You use Dynamic Data Exchange (DDE) to integrate a program into Windows Internet Explorer 7. In this program, you configure some options to open links in new Internet Explorer windows. However, when you try to open a link in a new window, Internet Explorer 7 opens the link in a window that was already open.
This problem occurs if you configure Internet Explorer 7 to open links from other programs on a new tab in the open window.
http://support.microsoft.com/default.aspx/kb/938526