If you've never used the disk with linux before, you're probably going to have to format it. I think there's a program for it in kde for it, but it's really not too hard to do from the command line:
#for high density, 1.44MB floppy
#"ls /dev | grep fd0" to see your other options
mount /dev/fd0 /mnt/floppy
Now you can copy anything to /mnt/floppy and it'll be on there.