VS 2010 - Scraping Website That Uses Ajax

We have a site that was scraping a site to gather all models available of a product. The 3rd party site recently changed the website so it now uses ajax for users to select the manufacturer and then once they select that it loads a dropdown with products using ajax.

I currently was using httpwebrequest for all requests (see below).

Code:
Public Function fnRequest(ByVal sPOSTData As String, Optional ByVal bAutoRedirect As Boolean = False) As String
Dim uriSite As Uri
Dim sReturn As String
Dim srReader As StreamReader
Dim sTemp As String

[Code] ....

Now in fiddler the post appears to be done with ajax. I tried to send the post data the normal way but it didn't like that. Any example of how to do this? To get an idea go to [URL] ... and see Mount finder and select Projector.