I have made some very passable negatives using inkjet printers and various kinds of clear substrates, which I have used for cyanotypes and regular silver gelatin contact prints; I see no reason why they wouldn't work for platinum/palladium printing. My experience with platinum/palladium is very limited, due to the high and rising cost of materials, but the general practice of taking images made with smaller formats and/or digital cameras and producing large negatives for contact print processes is sound. The trick is getting the densities and the tonal gradations right. This does require working in 16 bits or larger, in my experience. One interesting point is that you can use very cheap materials. I have made some very good prints from negatives printed on very cheap clear plastic mylar from an office supply store. The negatives don't have to last long, as you can keep the "original" digitally.
This is a technique I've been using for eight years; I started doing this as a way to teach workshops in cyanotype to people who didn't neccesarily have LF negatives. After some experimentation, I found it to work very well.
As for where to learn about platinum printing, the photographer George Tice claims (probably somewhat dubiously) to be responsible for bringing platinum/palladium printing back from the edge of extinction in the 1960's or 70's. He did publish a how-to article in a photo magazine back then, and he has since had at least one article on the subject published in View Camera Magazine, in May of 1989. Dick Arentz has published a fine book, "Platinum and Palladium Printing: A Complete Guide" which you should be able to find. If you are lucky, you might be able to find a workshop or course on the subject at Maine or Santa Fe or one of the other usual workshop suspects, but don't hold your breath. Most likely your best bet is to read as much as you can. Maybe you could write or call some of the folks working with the medium and try to pick their brains if you are serious enough about it to make a pain of yourself. The point is that you are going to have to work for this one, but you might come up with some amazing results. I can tell you that my unexpected forays into cheap digitally enlarged negatives have yeilded some wonderful and fun results. Good luck!
