Keep IE7 From Loading Until You Are Ready
Microsoft has had a utility available to help organizations block the automatic update to IE7 for a few months now. It just creates a registry key and turns off the ability to update automatically and blocks receiving the update through the express option on Windows Update. You can get the Toolkit to Disable Automatic Delivery of Internet Explorer 7 here . It also includes a group policy administrative template to help you do this accross your domain.
The folks at Intelliadmin have created a nice utility to help everyone else do it using their mouse! With their IE 7 blocking tool, you can do any computer you have an account on.