Where do files "go" when they're uploaded, and how would I access them in a VB.net class?

Here's what I'm trying to do...I'm trying to create a means of being able to output the content length and uploaded length of a file in VB.net to an XML file so that I can use it to create an upload progress bar.
I can write the XML part of it no problem.  I can also create the progress bar using jQuery without any problem, either.  Where I'm stuck is at this part (from the code-behind of the XML page itself):
 
Sub Page_Load(ByVal Source As Object, ByVal e As EventArgs) Handles MyBase.Load Dim Content_Length As Integer = 0 Dim Posted_Size As Integer = 0
' This is where I would access the uploaded files, but this is on a separate XML page. I suspect it's in the memory stream somewhere, but how would I get at it?
Dim settings As New XmlWriterSettings() settings.Indent = True settings.NewLineOnAttributes = True New_Doc = XmlWriter.Create(Respon ...