To rack mount your CDG Player, all you need is a shelf like this:
http://accessories.musiciansfriend.com/ ... sku=421306
Just measure the size of your player (vertically) and be sure to get the right size shelf. The one I linked to is a 3-space shelf, you might only need a 2 space shelf. Remember that each rack unit (space) is 1.75 inches.
Then for switching between 2 video sources, I'd recommend a hardware solution. Get a smart switch similar to this one:
http://www.amazon.com/Philips-PH-61153- ... B000165AOY
On there you set one video input as your default source (the PC) and it will automatically stay on that source until another source starts sending a signal (the player). So you'd keep the player turned off except when you need it.
Use two separate channels on your mixer for the audio from those two sources or you could run them through that switch as well.