PCs have never had their own CD ROM format. They use ISO9660 with or without Joliet extensions, and possibly UDF. OS X deals fine with such CDs (as does Linux).
There's a fairly decent chance that the media itself is damaged, or the disc wasn't burned within the tolerances that the Mac permits for CDs. Some drives are sloppy than others on writing, and some stricter than others on reading.
It's possible, depending on the age, that the disk has succumbed to one or another of the various problems that damage the media: UV damage from sun exposure, scratches, thermal damage from proximity to heat, oxidation of the silver substrate, degradation of the organic dye, surface deterioration from xylene or toluene from permanent markers used to label the disk, improper lamination, etc.
Inspect the reading surface of the CD-ROM and look for irregularities in the coloration or reflectivity of the disk across the surface. Any variation indicates some degree of disk rot. The close to the center of the disk, the lower the chance that any of it will be readable.
