I'll give this a shot...
On you Powerbook you will have a folder in called iPhoto. This is a library of you pictures, keywords, tags, titles and any other details that you use to organize the pictures in iPhoto. Basically this is the folder (AKA Library or database) that iPhoto uses this to maintain how you organize within the iPhoto applicatio. This folder is located in your home directiry ie. /user/Pictures/iPhoto. With that said this is the folder that you will copy to your new computer, either thru firewire target disk, copy to external disk drive or thumb drive, or over the network.
These steps are assuming that you do not have any pictures in the new Macs iPhoto that you are keeping.
Step one
On both the old and new Macs, Make sure iPhoto is not running.
Step two
On your new Mac, rename the iPhoto folder to "org iPhoto" with out the quotes. This way if something goes wrong you can get the old library back.
Step three
Copy, do not move, the iPhoto from the old Mac to the new Mac using thumb drive, firewire etc. as mentioned above. Place the iPhoto folder from the old Mac into the same folder "Pictures" where your renamed folder "org iPhoto" is located.
Step four
Once the old Macs iPhoto folder (library) is copied to /users/pictures, open the iPhoto application.
Step five
iPhoto may tell you that the library is older than the current application and it will need to convert or update the library. Let it do the conversion.
Step six
Go get coffee as this may take awhile.
Step seven
Well if it finished the update or conversion with not errors than you are done.
Anyone, feel free to correct anything that is not accurate. But do not worry this is pretty close.