maybe a dns compatibility issue....
maybe you can try to enter other dns servers in your router config.
ip config -> wan & lan -> WAN DNS Setting
I've very good experience with opendns which is free, but it requires registration I think: http://www.opendns.com/
or google dns which is also free: http://code.google.com/intl/en-GB/speed/public-dns/
or ofcourse another public dns you like...
it sorted a lot of slow performance dns requests over here