First page launches a pop up window to show an animated GIF. Must do a pop up since IE chokes and stops all GIF animations when asked to do something else on the page.
When the data gets submitted, your 2nd page will load. Have that page run JavaScript to close the pop up window you opened.
As for cancelling, the user can click stop or go to another web page. I don't know if JavaScript can interact with the browser and issue a "stop", but in theory, you could add a link to the pop up to direct the user to a different page in the main window which should stop the upload (in theory, of course).