You may use
Update Panels to acheive this or use
JQuery. Jquery will completely avoid postback action by making a javascript call to the server when update panel will postback only what is inside of the update panel and will avoid a complete postback (and also the pageload).
However if your goal is to avoid some actions in your pageload event I would suggest you to use
IsPostback property wich will be set to true when the server call comes from a postback.