After googled at bit, i've found that newer libgpod (svn version only !) can support newer iPods. I've so rebuild it (as well as gtkpod itself) and packages are now sitting in my testing repository (only for i386 at this time, x86_64 will follow)
Attention, you'll have to remove first the libgpod package (if already installed) with `yum remove libgpod` (it will also remove rhythmbox !) and then you can install gtkpod and libgpod (svn version)

You have to know also that to correctly write informations in the iTunes DB file sitting on the iPod, gtkpod needs to know the 'FireWire id' of your iPod. You can easily discover it with `sudo lsusb -v|grep -i serial` . Write the 16 character long string down on the iPod so that gtkpod knows it for a correct synchronisation. For example , mine is 000A27001A484CF8 so i created the following file /media/ARRFAB\
IPOD/iPod_Control/Device/SysInfo (Arrfab Ipod being my iPod's name in case you were wondering ... ) with the content being : `FirewireGuid: 0x000A27001A484CF8` (notice the 0x in front of the 16 characters string) .

Now you can fire up gtkpod and upload music to your iPod .... Enjoy

I'll try to put it in the clean repo but because it will overwrite a base package, i have first to find the correct way to do it ...

Gtkpod in action on CentOS