Enabling html in textbox using Server.HtmlEncode

I there, I am trying to create a simple blog and want to use some html tags but right now i get a "A potentially dangerous Request.Form value was detected from the client (ctl00$body_placeholder$pst_summary="<em>More than 60 art..."). " error.

 I know I am supposed to use Server.HtmlEncode but where do i use it? and How do I use it? Please help.

 Here is the code:

 1 <%@ Page Language="VB" MasterPageFile="~/admin.master" Title="Manage Articles" %>
2
3 <%@ Import Namespace="System.Data" %>
4 <%@ Import Namespace="System.Data.SqlClient" %>
5
6 < ...