Yes! and very easily.
So your Powerbook is using the Airport card so you'll have to share the network through a wired ethernet cable.
On the powerbook go to System Preferences> Sharing, and find the Internet tab at the top. Under this you'll select Share internet connection on Airport and then check the box for Built-In Ethernet.
Now connect your iBook and PB together and set your iBook for an ethernet connection and you're all set.