IWebProxy proxy = myWebRequest.Proxy;

string GetEnabledProxy()
{
    string res = "";
    try
    {
        RegistryKey registry = Registry.CurrentUser.OpenSubKey("Software\\Microsoft\\Windows\\CurrentVersion\\Internet Settings", true);
        object proxyEnable = registry.GetValue("ProxyEnable");
        object proxyAddr = registry.GetValue("ProxyServer");
        int inProxyEnable = 0;
        if (Int32.TryParse(proxyEnable.ToString(), out inProxyEnable))
            if (inProxyEnable == 1) res = proxyAddr.ToString();                
    }
    catch (Exception)
    {              
    }
    return res;
}

string proxy = GetEnabledProxy();                
if (proxy != "")
{
    MessageBox.Show("Proxy: " + proxy);
    IWebProxy iProxy = request.Proxy;                    
    WebProxy myProxy = new WebProxy();
    Uri newUri = iProxy.GetProxy(request.RequestUri);
    myProxy.Address = newUri;
    myProxy.Credentials = new NetworkCredential("user", "password");
    request.Proxy = myProxy;
}
else
{
    MessageBox.Show("Proxy is null; no proxy will be used");
}