So the only thing I could get to work was...
Add an Airport Express and have it create it's own network. I can only get WEP security to work with the iPhone4.
I changed my DHCP scope on my main router to leave room for a static IP for the new Express.
In summery what I now have is:
Time Capsule running 802.11n 2.4 and 5 Ghz (Static IP)
iPad (Gen 1)
AirPort Express running 802.11n (802.11 b/g compatable) 2.4 Ghz (Static IP)
I will see if my iPhone 3GS connects when it gets home tonught.
I did try to extend my network with the AirPort Express but it would only support the 5 Ghz network.
Thanks you for the quick reply randers4 but I have been reading the forums most of the day and tried all kinds of things aready.