Configure OpenDNS on Apple Airport with Sky broadband

It seems to be impossible to (easily) point the current Sky broadband routers to OpenDNS, but I want to make OpenDNS the default on our home network. There are too many devices and people coming and going to configure individual computers and handheld clients, so that's not a practical solution.

However, I already have an Apple Airport network running through the house with one Airport Extreme in 'Bridge' mode connected to the Sky box by ethernet. That all works fine, I do not use the Sky wireless but the Sky box handles NAT and DNS, so everything is currently on the same 192.168.0.xxx network.

I can do a lot of trial and error, but I'm sure others must have cracked this. How do I configure the Sky box and the Airport so that the Airport handles DHCP and becomes the router from which connecting devices look for DNS information by default?

Obviously I can put Open DNS's server numbers into the Airport configuration, then I imagine I switch the Airport out of Bridge mode into with DHCP or DHCP&NAT mode (but which?) and assign a new range of numbers (e.g. 192.168.1.2 to 192.168.1.250) for the Airport to serve. But how will the Sky box react? Does the Airport need a fixed IP address in the 192.168.0.xxx range? Or can you just keep passing DHCP services down the line? And does any of this affect performance?

Any help much appreciated!