I'm no idea what's inside the Belkin Tunetalk, but there's a patch on the patch tracker which contains my work so far on ipod recording:
http://www.rockbox.org/tracker/task/6096This will require a little work on your part to test - you'll need to apply it to an older version of the Rockbox source code (recent changes to the generic recording code will have broken the patch) and compile your own Rockbox build.
If the Belkin Tunetalk is just a simple line-in adapter, then there's a good chance it will work. However, if it tries to communicate in any way with the ipod via the Apple Accessory Protocol, then more work will be needed - Rockbox doesn't support such communication yet.