Thanks, worked like a charm. I suspected something like this.
Now for the fine art of figuring out whether the girl or her younger brother is the culprit.....
My daughters iMac recently started behaving strangely when connected to the home network. It connects ok to both wireless and wired networks, and recieves dhcp address from the router ok. Then after a few seconds of use it stops performing name resolution. After some searching around I've found...