Custom Dialog in Sharepoint 2010

The easiest way to show this is with an application page.

<asp:Content ID="Main"
ContentPlaceHolderID ="PlaceHolderMain"
runat="server">

<script type="text/javascript">
function ShowDialog()
{
 var DialogOptions =SP.UI.$create_DialogOptions();
 DialogOptions.url="http://www.google.com";
 DialogOptions.width=500;
 DialogOptions.height=400;
 DialogOptions.dialogReturnValueCallback=Function.CreateDelegate(null,CloseFunction);
}
function CloseFunction(results,target)
{
 if (results == SP.UI.DialogResult.OK)
 {
  alert("You have clicked OK button");
 }
}
</script>
<input type="button" value="Show eMids" onClick="ShowDialog()" />

</asp:Content>