I kind of assumed that he (or she, you never know,) had a SCSI CD-ROM drive, but no dock to give SCSI to the Duo.

But, yeah, a 5300 doesn't have an internal CD-ROM drive, so to use any CDs, you'll need a SCSI CD-ROM drive for that 5300. But, the 5300 can take a PCMCIA Ethernet (or even WiFi) card, so you could have a horribly convoluted three-way sharing, if needed.