2.0 -how To Include Files Containing Server-side Code

I want to be able to load a customized log in page depending on a couple of parameters passed into the querystring.Each customized login page needs to be able to dynamically display log in errors and possibly have other variables passed in.
Let's say the dynamic login page looks like this (over-simplification here):

<form>
<% if (has_errors) { Response.Write(error_msg); } %>
<input type="text" name="email">
</form>
If the aspx page loads the file like this:
Response.writefile("path/to/custom/page");

the code shows up in the output and doesn't get processed. I have tried other ways to load the file contents (something similar to classic ASP includes) but get the same results every time.I could have all the custom pages set up as user controls, but I need 100% control over the css, js, and html - and the documentation I read here indicates that I won't have that level of granularity.link textPLUS - I'm stuck in a .net 2.0 environment - so .NET MVC is not available to me