Depends on how old (or new) your PowerMac is. Roxio Toast Titanium 6 is the only CD authoring software I know for the Mac that has the "shared recorder" (ToastAnywhere) feature, but it requires at least Mac OS 10.2 (Jaguar). If your PowerMac is capable of running Mac OS X, then ToastAnywhere will suit your needs.
Both Macs have to have Toast 6 installed on them, and both should support Rendezvous. Your PowerBook will be able to "find" the shared recorder, and can use it to burn the files from its hard disk to the CD-R.
The long route would be to copy the files across the network then burn from the PowerMac. You can lessen the amount of shifting by installing remote management software (like VNC, which is free, or Apple Remote Desktop). You connect to the PowerMac from your PowerBook (through an exported screen) and then control the PowerMac over the network. Not as seamless, but it works.