WebBrowser and proxies

I'm using the WebBrowser control, navigating to certain URL using the "Navigate" method like this:

Dim header As String
header = "Proxy-Authorization: Basic YTkyNDA2MDp0b21hdGl0bzQ=" & Chr$(13) & Chr$(10)
myBrowser.Navigate "http:\\www.terra.es", , , , header

As you can see, I add login information to the header, using the last parameter of the method navigate. This way the proxy doesn't ask for user log in as long as the user name and passwords that are encoded in the header are correct.

But there is one problem: if the web page that we want to open contains images, the proxy asks for user name and password for each image in the web page... Any ideas to solve this?

Thanks in advance.