check_http with proxy authentification

Hi,

I'm trying to check a website trough a proxy server that requires me to log on 
using nt credantials domain\user password.

I know how to use a proxy server but I can't figure out the authentification 
part.

This is what I have at the moment:
check_http -H http://www.cnn.com -I proxyserveradress -p 8080
this hives me the following error:
http ok: http/1.1 407 proxy authentification required ( the ISA server requires 
authorization to fulfill the request. Access to the Web Proxy service is 
denied.)

The proxy server is a Microsoft ISA proxy server.
Any help would be great.

Greetings

Wim



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