use can use inbuilt Tool tip felicity, and use ScriptManager on the page where you have designed for the MS Chart
<asp:Chart ID="chtProducts" runat="server" ...>
<Series>
<asp:Series Name="SalesByMonth" ChartType="Column" BorderWidth="5"
ToolTip="#VALX{d}, #VALY{d}"
ChartArea="MainChartArea"
YValueMembers="Total"
XValueMember="Month"
PostBackValue="#VALX" />
</Series>
<ChartAreas>
...
</ChartAreas>
</asp:Chart>