remove isp-provided dns

My isp provides a dns service; but unfortunately they do block certain sites.
I would like to use opendns or google; but it seems like it doesn't work.

I have set up a wired connection; given a manual ip and entered opendns-ip's in the nameserver field (all through the gui).
Still url's are being resolved through my ISP.
I have tried to configure the same on my girlfriends laptop (win 7) and I also can't seem to do the setup. My previous computer also was a win 7 and had no problem. (so I believe the problem is 'me')
If it were only one site, i could edit the hosts file; but I prefere to circumvent their whole dns server.

Is there something an isp can do to block the use of other dns-servers than theirs?
Is it possible to re-route the ISP dns to the opendns?

Solution 1:

I suggest you right-click the Network Manager icon and select Edit Connections. Under IPv4 settings, change the method to Automatic (DHCP) addresses only. Then fill in your preferred DNS nameservers. Please see: