Yep, this is typical of orphaned tech...Kodak has quit reving the software for importing Photo CD images (actually since Photoshop CS2 I think) so if you want to open those old Photo CDs, you better keep an old G4 or G5 with Tiger on it with Photoshop CS or CS2 to access the image packs...
Actually it was/ is still possible to copy the Photo CD.8BI plug-in from an earlier Photoshop version into the CS4 Plug-ins/ File Formats folder, thus to open the PCD files in CS4. No 64 bit support though (Windowz). The option to edit the resulting TIFFs through Bridge + ACR is a real gem.
… just in case someone around here struggles with the same issue.