All of the information, and misinformation, that I know of Crestron I've learned online.
Programming Crestron, I understand, is not brain surgery, it's just protected information. Crestron does a good job of protecting the line.
Not many people talk about it much, but it appears to me that dealers sell and install the equipment, and Crestron Certified Independent Programmers (CAIPs) do the programming. And, I've heard that you can't be a dealer AND a CAIP. The programming is farmed out to another company. There are many CAIP firms around the country who would be very happy to do the programming for your equipment.
There were 8-10 CAIP firms set up at CEDIA, showing their stuff. Really nice work, first rate. Of course, some better than others.
Some large universities and colleges employ their own CAIPs, and buy their own equipment, for lecture halls and such. I believe this may be a good source for Crestron software, if you're affiliated with a university.
Hard to become a Crestron-certified dealer, lots of hoops. I think it's relatively straigtforward to become a CAIP - I think you have to show programming experience, and attend some expensive courses. The courses may be free/cheap if you're affiliated with a university.
If I really wanted to DIY Crestron, I'd try to become a CAIP. Or join the university AV club.
Edit - keep in mind that Crestron is behind a great deal of commercial work. Many Crestron dealers/installers/programmers out there.
There is a Yahoo Groups for Crestron, and it seems many DIYers, I've heard, end up there.
Edit #2 - Daddy_Warbucks on AVS is having some DIY Crestron success,
interesting thread.