I was forced to sell my iMac G5

and had to resort to using my old Blue & White G3 for a while. I backed up all critical data, and thought I grabbed what I needed from the Music folder. Here's what I saved:
I've tried importing the above on the G3, but that hasn't gone well. Dragging and dropping all the folders under iTunes Music results in a complete song list sans library, but many of the songs are greyed out and iTunes says it can't find them. Obviously importing the library results in a duplicate of the library from the iMac but no song files.
I know all the songs are there in the iTunes Music folder, but just can't figure out the right way to import them properly. I suppose I should have done an export out of the iMac but in my haste I thought copying the files was good enough.
TIA for any advice, I'm not a Mac newbie but just haven't had to do much with iTunes up until this point...