I know they make a 2in 1 out but Im not sure they make a switch or a cable for that and if they did your gonna pay out the nose for it I would think. I checked monoprice and they had nothing with what your looking to do except maybe
THIS but is what you wanting to do worth the $300 to have the same show on 2 screens at the same time?
Why not use your computer and one of the d-sub or dvi outputs from your video card to the Projector? If you own a ATI card you can then go into properties and select it around to show the video on both screens at the same time and it wont cost you no more then a DVI cable. I cannot speak for a nvidia card if it can do this but if your look for a switch Im guessing your computer is close enough that you were running a cable from a dvd player to it.
I have my HT set up going from PC with a X1900 AIW. Its about 10 feet away from my PJ I just got yesterday. Instead of hooking up another dvd player to it and getting inferior picture I ran a external case with a 10' usb cable and a dvd rom. With that and the Remote that came with the AIW that acts like a mouse I can controll my pc from my chair and swap out dvd's and games. Games obviously wont run on both monitors at the same time or it does and I havent figured it out yet, but this may help you as an alternitive. BTW using this way and the free VLC player it outputs to my Optoma H31 at 1280x720 same res as my dying Cyberhome upconverting dvd player does when using the HDMI/DVI adapter and looks better too IMO. For sound I use my digital out and a 20' toslink wire running to my audio amp.