John,
Thanks so much for your response.
I'm using "referenced" to indicate that the raw files were originally imported by reference instead of by "copying" into LR.
I have a Catalogue on both the laptop and G5. All the pictures are in the recorded in the catalogues. I edited, and rated all the images. Many have been cropped and worked on the the Develop Module.
Mitchell
There is no concept of "copying into LR". You either import them by adding them where they are, which you are calling "referenced" (Aperture uses that term) or you import them by copying/moving them to a folder other than the one they were in at the start of the import process. You do need to get clearer about this. Anyway....
OK, start with whichever machine has the fewest pictures, so you get an idea of the process. Copy its catalogue (the whole folder with the lrcat and the related lrdata file) and the picture folders over onto the new computer. Then on the new computer, double click the lrcat file and check that you have no question marks in the Folders panel. If you do have, that's because the path to those folders doesn't match what was on the other computer. So click the question marks and point the catalogue to where they now are. So now you have your main working catalogue with half of your pictures correctly "referenced".
Bring over the other computer's catalogue ("source2") and pictures over to the Macpro, and then in your main working catalogue go File > Import from Catalogue and point to source2. It will then import source2's data and register its pictures in your main working catalogue.
You can then delete source1 and source2. Everything is now referenced in one main catalogue.
John
ps I assume the MacPro has no pictures on it yet, and no LR catalogue (or at least only an empty one)