The iBook and the Mac Mini are designed specifically for first time Mac users, and Mac users on a budget. The great thing about these two Macs, is that they are just as powerful as the top-end Macs when configured correctly.
If you want power on these budget machines, the iBook needs 1.5gb RAM (You will just need to install a 1gb RAM card, 512mb are already on the logicboard.)
The Mac Mini needs 2gb. It comes 512mb. You will replace the factory installed RAM with 2x 1gb Chips.
Current PPC Speeds:
iBook: 1.33ghz w/133mhz FSB and 1.42ghz w/142mhz FSB
Mini: 1.25ghz and 1.42ghz both w/167mhz FSB
Current Intel Speeds:
Mini: Core Solo @ 1.5ghz/CoreDuo @ 1.66ghz both w/667mhz FSB