[Staffslug] An unanswerable question!

I had been using LiveCD's without a problem - any I tried would pick up a DHCP address and go out to the internet - no problems. Suddenly they stopped working. No matter what distro I use now - I still cannot access the internet. I tried getting an answer to this on the ubuntu forums but they couldn't help! I am picking up an IP address (via DHCP) with no problems - whether I'm using wired or wifi (to an Apple Airport express AP which gets it's own IP through DHCP) but cannot get online. After reading something unrelated earlier - I thought about pinging an IP address to see if I get a response. Tried pinging google.com and I always get a response. I then put the IP address straight into Firefox and got the page up. So, my issue appears to be a DNS issue with every LiveCD. It's odd that it doesn't matter if I use wired (straight to the router - a D-Link DSL 504T) or wireless through the Airport Express AP > DSL504T. To complicate matters - if I use my Powerbook (running OS X) with wired or wireless - it works fine. Also, if I use my tablet PC running Vista with wired or wireless - it works fine! Can anyone suggest anything? In my DHCP settings on my router, it's giving the DNS address as the router address. is this correct or should it be the DNS address of my ISP? Carl