You can use aspnet_isapi.dll to run your classic asp vbscript applications without code-behind and without the normal restrictions of asp.net. I have successfuly converted a major classic asp application to asp.net without changing any of the architecture, without adding a single new file except the web.config. The key is understanding the scope of <% %> and <script></script> code blocks.
Classic asp vbscript code and vb.net asp.net code is very very similar. There are only a few simple syntax changes you will have to make. Your includes will still work no matter how complex they are.
If you're tired of using the asp.net web controls and the restrictions of a using form runat=server and events, this way of using asp.net is for you. Take back control of your website and use asp.net the way you want to use it!