It sounds like you want to postback only a portion of the page using JavaScript. According to
this page, you can do that like so:
<asp:ScriptManager ID="ScriptManager1" runat="server" />
<asp:UpdatePanel runat="server" ID="UpdatePanel1" OnLoad="UpdatePanel1_Load">
<ContentTemplate>
<asp:Label runat="server" ID="Label1" />
</ContentTemplate>
</asp:UpdatePanel>
The UpdatePanel is required to postback only a portion of the page. The ScriptManager is necessary to use any AJAX stuff (in this case, the UpdatePanel). The Label is for demonstration purposes.
<div id="Container" onclick="__doPostBack('UpdatePanel1', '');">
That shows how to make a postback for just one UpdatePanel from JavaScript. In this case, it is initiated from a click event.
protected void UpdatePanel1_Load(object sender, EventArgs e)
{
Label1.Text = DateTime.Now.ToString();
}
That shows how you can use server-side code to update the client during your UpdatePanel postback.