the following example shows how to refresh part in asp.net page every 0.5 second using asp.net ajax
<form id="form1" runat="server">
<div>
<asp:ScriptManager ID="sm1" runat="server" />
<asp:UpdatePanel runat="server" ID="up1">
<ContentTemplate>
<asp:Label ID="currentTime" runat="server" /><br />
<asp:Timer runat="server" ID="refreshTimer" Interval="500" Enabled="true"
ontick="refreshTimer_Tick" />
</ContentTemplate>
<Triggers>
<asp:AsyncPostBackTrigger ControlID="refreshTimer" EventName="Tick" />
</Triggers>
</asp:UpdatePanel>
</div>
</form>
protected void refreshTimer_Tick(object sender, EventArgs e)
{
currentTime.Text = DateTime.Now.ToLongTimeString();
}