For anyone who cares about the hiccups I encountered here is what happened.
I connected the printer and hard drive to the Airport and then plugged it in to the power. I then followed the set up instructions and created my network. So far so good. I re-routed my printer address in my settings and tried the printer, all good. Then I tried transferring and accessing a file to the hard drive, again good. Then I tried connecting to the internet and it was a no go. Disconnected Airport and I could get on the net but I couldn't do both at once. Spent quite sometime looking for a solution on the net, changed a pile of settings. Managed to get on the net with Airport on only I lost access to the hard drive. So I had to reset the Airport and then I decided to upgrade my Mac OSX to Snow Leopard which I had but hadn't installed yet in the hope that would change things up. Well it did. I successfully managed to loose all access to my internet as the dongle software isn't compatible with Snow Leopard! So more internet searching and a trip back to the Mac Shop and I managed to manually configure my dongle and get onto the net. It was Airport or the net again but a few more tweaks and FINALLY I can access both the internet and Airport at the same time. Phew, lots of work but worth it!