I think you cannot program your own applications with the default Apple os iPod ships with. Instead you might want to add linux for iPod (http://ipodlinux.org) to your iPod (and have both Apple iPod OS and iPodLinux): This way you can definitely start writing your own apps and modules for your iPod (using c++)
Programming for iPodLinux is easier than you think. You have to already have a good working knowledge of C, but it's doable. I wrote a few apps actually.