Jesse
Brad makes a number of good points regarding the complexity of a projection system, and the need to bring in some seasoned expertise. But, a good place to start is to start making a block diagram that will provide a road map for the signals. Draw signal flows left-to-right, with sources on the left and projectors on the right.
FormatsYou will start with essentially two types of video signals, NTSC (National Television Standards Committee) interlacing video, and RGBHV progressive scanning video; the two don't mix. The NTSC sources (camera, DVD, or VCR), can be cabled in composite, Y/C (S-video), or component (think "good, better, best"). The RGBHV (red-green-blue, with horizontal & vertical sync) can terminate in the 25-pin high density connector, or in 5 seperate BNC connectors.
Seamless Switchers convert the NTSC to RGBHV, and then permit switching between RGBHV sources. Some manufacturers of seamless switchers are Extron, Kramer, Analog Way, and Folsom. If the computer and DVD player is next to the seamless switcher in the sound booth, the switcher will serve as an interface and switcher.
PC InterfaceHowever, if the computer is located onstage, signal degradation can occur after the signal travels a long distance, so its advisable to employ a PC interface. The interface boosts signals, provides horizontal adjustment, and provides a buffered output if you need a local monitor.
Cabling between the output of the seamless switcher and the projector can either be 5-pair coaxial, or CAT-5e type (think computer network) cabling. The CAT-5 type requires a set of encode-decode electronics on either end that translate the RGBHV to the RJ-45 connector(s). There is a case for either kind of cabling, based on cabling length, ease of cable routing, conduit availability, etc.
Cue MonitorWhen you design your system, make sure you have a cue monitor scheme for every source in the booth. For instance, you might want to cue up DVD program "behind the scenes: without needing to show the image on the projector at that moment, so a dedicated monitor or TV would be appropriate. And likewise, it's nice to know what the computer is outputting before you unblank the projector, so a monitor that displays the output of the computer makes sense.
ReferenceExtron is considered by many to be the industry information source. I recommend that you spend a lot of time on the web site looking around at the different devices, glossary, articles, etc.