display modal popup with minimize and maximize in asp.net

Question

hi sir ....i am displaying a modal popup when link button is clicked.........please help me how to add those two properties..please help me sir

my aspx code:

<script type="text/javascript">

 function OnClickChat() 

{

 window.showModalDialog('ChatWindow.aspx', 'dialogHeight:450px;dialogWidth:506px;state:maximize;');

 }

</script>

 <asp:LinkButton ID="lbtnUserName" runat="server" Text='<%#Eval("UserName")%>' OnClick="lbtnUserName_Click"  Font-Names="Bertham" Font-Size="Small" CommandName="selectlbtnUserName" Font-Underline="False" ForeColor="Blue" Visible= "true" />

            codebehind:     

  protected void lbtnUserName_Click(object sender, EventArgs e)

    {

        ScriptManager.RegisterClientScriptBlock(this, this.GetType(), "scr", "javascript:OnClickChat();", true);

    }