Sorted, 3 days later......
Basically I installed a network card so i could connect to my existing set up (Mac and Router) using ethernet. That's when all the fun began, apparently adding an NIC causes a reactivation to be required, but somehow buggered the IP settings on the computer. I eventually used the phone number and got it all back under control.
The router was operational all the time and so i knew it wasn't that.
What a farce, I'm sure that people love XP, but i'm sticking with Mac.
Thanks, Shaft