VS 2008 - How To Read IFrame Hidden Input Value

I'm using jQuery to build an IFRAME and pass some hidden input values to a Download.aspx page - jQuery code looks like this

Code:
$('<form action="'+ url +'" method="'+ (method||'post') + '" target="iframeX">'+inputs+'</form>')
.appendTo('body').submit().remove();

The inputs variable looks like this

<input type="hidden" name="filename" value="mit-license.txt" />

And the top of the Download.aspx code behind looks like this

Code:
Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
Dim ctx As HttpContext = HttpContext.Current
Dim response As HttpResponse = ctx.Response
Dim sFile As String = "mit-license.txt" ' Request.QueryString("filename").ToString

[Code] ....

I could not find the INPUT value - where does it pass in? I checked the "sender" and the ctx objects and could not find it... I hardwired the mit-license.txt filename to prove that the download works...