When you get your new iMac, there is now a utility app called "Setup Assistant". It starts instantly when you first turn on your iMac. It will ask you if you have another Mac that you want to use to transfer files to your new iMac. It will have you attach a firewire cable to both macs so you can go into the target disk mode.
In a short period of time you will have your documents and apps transferred over. You may have to reinstall a few apps from your original disks but these will probably be very few in number.
Transferring from your iBook, you may find that a battery menu shows up in the menubar of the iMac. Just remove it if so.
Congrats.