run method after page_load

I have a page that requires 10+ seconds to load as its doing a lot of web service processing before the page is displayed. I am currently doing all of the in the page_load event. While this is loading the user just get a blank page while all the processing it happening as its 10+ seconds I want to display a message saying please wait while we process your details with a spinning wheel gif so it doesn't look like the page has froze and stop the user refreshing the page. When I try doing this in the page_load event the message isn't displayed as nothing on the page is displayed until the page has finished the page_load event.

How can I reslove my problem displaying the message on the page first, then automatically run the method with the long processing without any input from the user