Hi Mark,

One of the easiest ways to do this is through the Asp Ajax libraries.

For example, create a simple html button that calls a js function Process()
when clicked.

Within Process(), you want to add the javascript to show your 'processing'
message, and then call your server side code. You can call this code by
turning it into a web service, and adding that web service to the page's
script manager. This will let you call that web service very simply through
javascript.

If you want to cancel processing, you'd need to create a new web service
that will hunt down the processing operation and shut it down.

If you're not too familiar with the asp ajax model, I suggest you check out
the documentation, particularly:

http://www.asp.net/AJAX/Documentation/Live/mref/P_System_Web_UI_ScriptManager_Se
rvices.aspx

Regards,
Andrew