"CD emulator"..umm that's a weird term. Do you mean you would like to be able to use a CD image file instead of a real in-drive CD? It depends on what you need, but you can mount a CD image file to a directory like this:
mount -o loop /home/fofire/cdimage.iso /media/cdrom
which mounts the image to be a part of the filesystem (change path and filename accordingly!) in /media/cdrom. That's how you would mount a regular cdrom too, except that with images you need the loop
option (and cdrom device file would be something like /dev/cdrom and not some .iso file).
If it's about games that do cd checks and so on, then I'm not sure if that's enough.