No. You don't need to change anything at DNS servers. Leave them be for now. Open your /etc/resolv.conf and after nameserver add any of those IPs I listed above (delete your own nameserver ip, which is listed there). Before doing so run:
and post output.

it's something like this :

Server: 193.140.?7.4
Address: 193.140.?7.4#53

1.0.0.120.in-addr.arpa name = localhost.

Yes, because something is either screwed up or "cleverly fixed" (a euphemism) by the admins.

For reference and the education of another poster, if you don't actually need a search domain, then don't just make one up, and definitely don't stick the name of someone else's host in there. That will cause a lot of useless nameservice queries to go out in their direction. Just leave the entry out of your resolv.conf. Nothing "breaks" if it's not there, and if nothing else since the host won't have an extra name to lookup as it walks the domain search list, it will resolve faster in those cases.

By the way, we all know you're talking about doubleclick. There's no point in trying to obfuscate things. And please, in the future, write these things down when we ask you for information. If your nameserver really is returning "1.0.0.120.in-addr.arpa" something is completely fried beyond belief on either their end, or your RAM is cooked. Mainly I just think you're not putting much effort into reporting results exactly because you don't know which parts are important and which parts aren't.