Making a Mac/PC hybrid CD-ROM is not as dark an art as some would have you believe. It's a good idea if Macs are part of your audience, though you'll have to author on a Mac. Every production Mac should have the free Joliet extension from www.tempel.org/joliet/ to make it possible without it, Mac's won't see long Windows filenames on CDs. I'll cover Director authoring a little later this first guide assumes identical contents on Mac + PC.
Use Disk Copy to create a new image from the folder containing your entire disc. If you've made an ISO first, just mount it on the Mac (with the Joliet extension) and create an image from that.
Mount that new disc image on the Mac. Double-click and position the open folder where you want; views, icon positions and window size/position are remembered. Close the window if you don't want it to open when the disc is inserted.
Launch Toast. Select Mac/ISO hybrid. Drag the mounted Mac volume (not the file containing the image) to the Toast window. It becomes the Mac disc image.
Then open the mounted Mac image, and drag all the contents (select all, drag) to the Toast window. They will become the PC disc. The clever bit: because the files have been dragged from the disc that the Mac side is coming from, the files will be shared on the final disc, not just written twice. Important.
Write Disc. Only use Write Session if there's space left on the disc and this is for internal backups only. Always use Write Disc for masters.
Director-based cross-platform authoring is similar, just requiring a little more organisation.
Create the project to launch from a stub movie a one frame, one script wonder that launches the first Director movie we want to run. We need to make a Mac and a PC projector from this movie. Compress other movies as .dxrs, put them inside a MEDIA folder. The stub sits outside this folder, but launches a movie within it.
Make a Mac disc image as above. Put the cross-platform MEDIA folder with any generic ReadMes, any Mac-specific ReadMes, and the Mac projector. Position the window appearance to make the projector and ReadMes obvious; hide the MEDIA folder out of view if you want to.
As Step 3 above.
Drag only the cross-platform contents to the Toast window for the PC-side. Also drag, from elsewhere on the drive, the PC-specific ReadMes, Projector, etc.
Step 5 as above. Macs see only Mac stuff, PCs only PC stuff.