I'm not sure if you can do it in the html source side, but you can add to the master page's header information in the vb side, everytime the page loads (postback or not).
Me.Page.Header.Attributes.Controls.Add(New LiteralControl("<script type='text/javascript' src='script.js'></script>")) The above code would dynamically add a link to an external javascript file. You can do the same type of thing with metadata, stylesheets, etc.
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MCP - Web Based Client Development .NET 2.0