OnBoardC is a C compiler that runs on Palm PDAs. That mean you can write programs for your Palm PDA on your Palm, compile them on your Palm, and run them. OnBoardC makes genuine .PRC files, so you don't need any kind of interprinter or anything. A file created with OnBoardC can run on any Palm device.
Writing programs for Palm OS is not difficult. On the other hand, you need to know C, and it help if you have experience in writing programs for event driven systems (like windows). There is a well documented API available, and you can find answers to almost everything you need to know in the documents.
There are also some documents included with OnBoardC. The first you should read is The OnBoard C User's Guide. Then you should look at The OnBoard C Programmer's Cookbook. The Cookbook is only half finished, but it is a really good document, if you ask me, and it helped me write my first program few hours after I downloaded OnBoardC first time.
I have bought a few books myself.
If you need help you are welcome to write to me and ask. You can also join the Yahoo group where we discuss OnBoardC.
Good luck...