Try doing

    mount -t cd9660 /dev/cd0a /cdrom

If that works, you can put

   /dev/cd0a  /cdrom  cd9660 ro

in /etc/fstab.

> Hello, I recently install NetBSD 1.4 on a Pentium 233.  I've been having
> some trouble mounting my cdrom, when I go to mount it (using mount -t msdos
> /dev/cd0a /cdrom) I get an error of Mount_msdos: Mount: Invalid Argument.
> The media I am using is a cd from cheapbytes.com and can be booted from
> (which leads me to believe I am doing something wrong in my mounting
> syntax).  I have attempted to mount using -t fat, iso9660, fs9660, and vfat.
> All of those return with an error of: mount: mount_fat(or put in
> iso9660/etc) not found for /cdrom.  I'm not sure what to do right now,
> seeing as how when I've used FreeBSD or OpenBSD it always found it and
> worked perfectly.  I hope you guys can help me out with this, and thanks for
> the time to read it.

Sincerely
-Thomas