Depends upon what kind of Ipod is it. If its the touch screen models then those are relatively easy to program(Although you need Apples SDK and pay for each program

) without Jailbreaking.
For the newer click wheels there is a project called FreeMyIpod.org and they have managed to crack all the way up to the 4Gen Nano, with code execution, serial and some of the basic stuff for most of the Nanos and some of the Classics:
http://www.freemyipod.org/wiki/StatusIf its a click wheel Ipod then depending upon what model and version, there are firmware replacements out their. There is a IpodLinux Firmware for some of the older click wheels and it has C programming support for it with access to the serial ports, video, audio, etc:
http://en.wikipedia.org/wiki/IPodLinuxThere is also another firmware replacement for the click wheels partially based upon IpodLinux, I believe they do have C programming support but are still just as open-sourced as IpodLinux:
http://www.rockbox.org/The only other thing that I can think of that is relatively official, but VERY expensive is Microchip's Iphone Development kit with their interface software/hardware kit.
http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=2018&mcparam=en547660Good luck