I had some basic unix knowledge from long time ago, this helped me to quickly take things up.
The document
here on the iRex website is a good starting point. You can follow the document and install Ubuntu yourself or use the VMware image published by Adam even on a windows PC (it is not as fast as a native machine, but for me it works).
On internet you can find a lot of information on GTK used for the UI of the DR (google for GTK tutorial). Start studying the helloworld example of iRex and the other programs that have been ported or written for the DR and published in this forum.
Also the published code of the DR by iRex is a good source of 'example' code.
Its basically a matter or just starting

.
Keep posting your specific questions here (or the iRex forum) I assume more people will benefit from the answers.