Proxy Authenticattion in C#

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C#

i am designing an application that accesses website for extracting data.. in my institute there exists a proxy, along with username & password this is the code i am using in app.config file
i am entering the proxy address in the settings for Internet Explorer


system.net
defaultProxy enabled="true" proxy bypassonlocal="true"
proxyaddress="http://website.com:8888/" /
/defaultProxy
/system.net

even then it does not connect to proxy...
1) i want that the application directly get the proxy ip from IE & access the net?
2) how do i pass the username & password to the application?
what is to be done?