Every time a new window is opened a place on the taskbar is also created for it. In your case, however, a window is being minimized to the taskbar automatically. When this happens:
1.) Does it only happen with IE7 windows or with windows from other programs as well as long as IE7 is running?
2.) Is it the new window that automatically minimizes or one that was previously open?
3.) If you click the minimize button on the currently-opened window do you see the other window afterward or do you still have to 'retrieve' it?
4.) Are you using IE7's tabbing feature or just separate windows?
I've noticed since I now have IE7 that when I have more than one page open a page will go to the taskbar and I have to retrieve it. Is this a bug in IE7? This never happened on IE6. It's like the page just disappears, which can be a pain if your working on it. I have WindowsXP SP2 media center.