C# application not respecting Internet explorer proxy settings

[Robb Gilmore]

WE have a C# .NET app which runs as a service.
It posts data to a server using HttpWebrequest.
According to the docs I 've read, it should use the proxy settings from IE
on the server machine. But it doesn't, it always posts straight to the
server.
I tried forcing it by doing this:

WebProxy defaultProxy = WebProxy.GetDefaultProxy();
webRequest.Proxy = defaultProxy;

But that doesn't seem to make it use the proxy settings either.
On the flip side, a client I have which calls webservices DOES respect the
proxy settings without my ever telling it to do so.
How do I get the HttpWebRequest to respect the IE proxy settings?

thanks
Robb