Just to make sure you're understanding this, vladimir88x7:
To copy files to Rockbox you don't use iTunes, and you don't usually need to convert anything, since Rockbox supports a wide range of formats - like OGG Vorbis.
To copy files, you just connect the iPod to a computer and copy files to anywhere on the player (except the .rockbox folder), like you would do with a pendrive or portable hard drive.
We strongly suggest that you read the Rockbox Manual if you haven't done so yet. It can be a bit long to read, but even if you only read the quick start section, it should already answer most of your questions.
http://www.rockbox.org/manual.shtml (select your player and the format you want to read the manual in)