Airport Base Stations usually come preconfigured to work under 10.x.x.x private address space, but you can change that editing the Base Station (ABS from now on) configuration with the AirPort Admin Utility. There are two easy solutions for your particular problem:

- OPTION A:
change your G4s' IPs to match the AirPort Network's IPs so all of them are in the 10.x.x.x so no routing is needed between them... but you will have to change the internal IP assigned to your ADSL o Cable router (you don't say what type of connection you have) because it sure has one in the 192.168.x.x range, like your G4s. You may have trouble if DHCP is enabled for the hole 10.x.x.x range, but can change that with the AirPort Admin Utility.

- OPTION B (preferred by me):
or you can edit your ABS Station configuration and so it works in the 192.168.x.x range. You don't say if your ABS is serving IPs to the iBooks or they are configured with static IPs. If you need the ABS to serve IPs under the 192.168.x.x range configure it just to handle part of that range (like ten IPs only) so they don't have conflicts with the IPs assigned to other machines or the router.

I hope this helps.

Hey thanks Yeti.. that looks promising.. You'll have to give me a few days before i can contact my client and try this solution.. will let you know.. thanks again.