The tool for extracting iPod firmware is called extract2g. Extract2g can be found on the Linux4nano SVN at http://svn.gna.org/viewcvs/linux4nano/trunk/tools/extract2g/. The Windows binary is provided, and the Linux version can be built with a simple make command. Extract2g supports all of the Nanos and the 5G and 6G iPods (haven't tested any others). If the output says something similar to "Extracting from osos.fw," you should be fine.
To obtain a list of availible files, type in:
extract2g -l dump.img
Please note that "dump.img" can be replaced with whatever your dump file is named. To actually extract the firmwares, type in:
extract2g -A dump.img
You should now have 3 files:
These are your extracted firmware images. To learn more about these, please visit the Firmware page. If you need more information about using extract2g, type in:
extract2g - -help
Also if you are using the osos.fw outputted by extract2g in iLoader you need to remove the 2 KiB header from it:
dd if=osos.fw of=osos.out bs=2048 skip=1
Or alternatively, under Windows open osos.fw in HxD and select 'select block' from the edit menu, select from 0x0 to 0x7FF, then delete this region and save.
Then put osos.out into /iLoader/osos.fw