I have a ASP.NET 1.1 web application page which is built with .net framework 1.1 and in GridView the data is displayed.
I want when they select multiple items then data is updated but without the complete postback of the page. Any help or suggestions please?
Wrap the gridview in an asp:UpdatePanel
See example here: http://ajax.net-tutorials.com/controls/updatepanel-control/
Best way to implement this in your scenario is write the code assuming you will do a full postback (ie on checkbox click, wire up a server event handler).
Once its all working with full postback, wrap the gridview in an UpdatePanel to achieve the partial postback.