http://www.mtu.com/
This is the website for you!
I make, play, and copy CD-Gs on my computer. I use microstudio.
CloneCD will copy CD-G disks. I use unsupported Lite-On burners to make my custom CD-Gs. Supposedly they won't work, but I found a method that works.

If you need help with anything, give me a shout. I'm not sure if there are any freeware programs that play Karaoke disks, but it might be worth a look.