I've never used Kubuntu (i think its one of those cd based distros, right?) and so cannot help on its specifics im afraid. What i would do is use the commandline, i.e.
cp /root/pinkfloyd.mp3 (or whatever) /media/usbdisk/pinkfloyd.mp3
or when i have a large number of files i use the command mc to open the midnight commander and copy the files from one window to the other.
Sorry i cant help more. You could look here: http://tuxmobil.org/player_linux_survey_creative.html