Also, the usual default permissions only allow root to mount/unmount removable media such as CD-ROMs and floppies. To change that, you'll need to alter the line in /etc/fstab that defines your CD-ROM's mount.
It should look quite similar to this:
/dev/cdrom /mnt/cdrom iso9660 noauto,ro,user 0 0
/mnt/cdrom is the mount point threadhead was referring to; your particular mount directory might not be same.
The "user" option at the end of the line is what tells the system that it's OK for a non-root user to mount/unmount CDs.