Connecting to …

everytime i open IE6 to get on the internet it gives me a logon window saying “Connect to ad.doubleclick.net” and askes me for a username and password (while it is asking me this
the page is still loading” then i clikc cancel and i can see that page normal but when i type in a new address it gives me the same thing…
and its getting annoing i always get that login when i try to surf the net
and its anoying…
if anyone could help i would really apreciate it
thanks,