You can also use the object tag in a similar fashion to what rjv has shown you for a standards compliant way

Code:
<object id="ExternalPage" runat="server" height="blah" width="blah">
Sorry, your browser does not support frames, please upgrade to a modern browser.
</object>

Code:
ExternalPage.Attributes.Add("data","http://www.mendhak.com/");