CompuServe Messages

I am researching IPAS development for the company I work for, JHT MultiMedia. Where can I get the basic information on how to obtain the developers toolkit, and what it takes to be a developer. I have noticed, that most of the commercially available IPAS routines seem to come from only a few sources. I won't be doing the development, but I don't want us to bite off more than we can chew. Any information you can give me or direct me to would be greatly appreciated.