iBook or MacBook? What kind of display out do you have? Is there any kind of display in on the G5? Can the monitor screen be isolated, or is it all one unit? For my purposes, I just purchased a $200 ViewSonic 19" HD monitor and hook it up to either my iMac or my MacBook using a mini-DV to DVI adapter. Works well, but you've got to check the specs first.
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"I am disappointed and deeply concerned that there is no objective evidence to support my position. So far."
- Spock 
If it's a G5 tower, then you need to utilize the VGA input on the monitor. IIRC there is no way for an iBook to output DVI, but I'm sure someone with more experience with iBooks will confirm/deny this.
If it's a G5 iMac, it won't happen.
Edit: Err sorry, you said "new iBook" so you're probably talking about the polycarbonate Macbook. Yes, those output DVI. Use the Apple adapter (will work) or the lesser expensive Monoprice adapter (mileage will vary - mine no longer works with my MacBook Pro)
If it's a G5 tower, then you need to utilize the VGA input on the monitor. IIRC there is no way for an iBook to output DVI, but I'm sure someone with more experience with iBooks will confirm/deny this.
If it's a G5 iMac, it won't happen.
Edit: Err sorry, you said "new iBook" so you're probably talking about the polycarbonate Macbook. Yes, those output DVI. Use the Apple adapter (will work) or the lesser expensive Monoprice adapter (mileage will vary - mine no longer works with my MacBook Pro)
Now I realize why they stopped calling the old laptops iBooks. They knew they would need that name in a few years for the iBooks App and the iBookstore. Clever clever.
__________________
"I am disappointed and deeply concerned that there is no objective evidence to support my position. So far."
- Spock