Hm, with WinRAR under Windows it is something like...
DraftPlease note I didn't test the script, it is just a draft. I had to write a backup script some time ago (that's why WinRAR but it is similar with any compress tool having command line options). But I am not any Windows user. Also no idea where user files for Ryzom client are stored, I would guess in users home directory somewhere (I am sure you can find this information here on forum :)).
REM Ryzom files backup script
echo "Starting backup commands..."
"C:\Program Files\WinRAR\Rar.exe" a -ag -m%LEVEL% %DST%\ryzom_backup-.rar %SRC%