How to show loading is in progress with the image using ajax

Hi
I'm using visual studio 2010 .net framework 3.5. 
In my project I'm importing excel file and it will take some time to load. 
So at this point I want to show something like a wheel that shows loading is in progress and make the screen read only.you might have seen in some webpages. 
so I want to know how to implement that. 
Please help me in this regard