Ok, it's a day later, we've had a lot of help with this and I feel an answer is very close to emerging. We've done away with the wireless aspect, incase it was this lovely big victorian house that was causing problems (it probably wasn't) but it's all ethernet cabled to the hilt.
I've flushed the DNS. I have the IP Config file to hand if anyone wants it (if it helps). We can ping sites but we can't see them and I have learnt an awful lot about internetty stuff recently, I just wish it workd properly. As ever, any thoughts??