Hi,
With most of these System-On-Modules (SOMs) There's normally OS pre-installed.
The X-scale SOMs more or less are compatible with most standard PC interfaces (PCI-compatible).
This means you can mount your system, interface with the necessary peripherals and ur application is ready for deployment (with little effort). You can install the necessary hardware and/or applications.
Of course, this depends on the type of application. You may want to override these features and do your own low level programming (development from scratch). You can do this in C or Assembly. The X-scale is ARM/Thumb compatible at the instruction level (ARMv4).
Added after 3 hours 15 minutes:
What specific application do u need to design? You can download the Data sheet and the developers guide. There's more information there.