I assume you're speaking of theatrical type projection rather than cinema or home theater or anything like that. There's a significant difference between working with video projection and being a projectionist.
Lighting and projection are strongly interrelated and can directly affect one another but there are typically very different goals and considerations involved. For example, in most projection applications you are also going to be dealing with the source(s), signal distribution and processing and so forth, so some knowledge of video is usually required that has nothing to do with the projection itself.
A lot of good general video information can be found online at sites like
http://www.extron.com/technology/index.aspx. A good place to get some hands on training might be with production and rental/staging companies as many of them do a great deal of corporate and concert related productions that include theatrical style video productions and presentations. They might be a good place to learn about some of the equipment and
practical considerations. They often need help with load in and out and in turn might let you hang around to learn some more. Also, InfoComm is coming up in June in Las Vegas, almost all the projector and related manufacturers will be there and there will be numerous classes that might be of interest.