you need the CD-ROM driver. I always use OAKCDROM.sys. It's free and you should be able to find a download somewhere.
you'll need to add this line to CONFIG.SYS:
DEVICE=C:\DOS\OAKCDROM.SYS /D:OAKCD
and this one to autoexec.bat:
mscdex /D:OAKCD
this assumes the driver has been copied to the C:\DOS directory; you can of course change it.
You can also use DEVICEHIGH if you wish. MSCDEX is a utility included with MS-DOS; if you don't have it for some reason it's available for free as well.