sorry if this has already been posted but for the nubs like me out there.
enable sshd from "about chumby" then press pi symbol
use putty to connect
http://www.chiark.greenend.org.uk/~sgtatham/putty/
once you're in the chumby via ssh or by plugging a keyboard into it
df -h
chumby:/# df -h
Filesystem Size Used Available Use% Mounted on
/dev/mmcblk0p3 118.2M 96.0M 16.1M 86% /
tmpfs 29.2M 596.0k 28.6M 2% /tmp
none 32.0M 76.0k 31.9M 0% /var
none 32.0M 0 32.0M 0% /mnt
/dev/mmcblk0p5 122.0M 4.1M 111.8M 4% /psp
/dev/mmcblk0p6 1.4G 191.9M 1.2G 14% /mnt/storage
none 32.0M 44.0k 32.0M 0% /dev
/dev/mmcblk0p6 1.4G 191.9M 1.2G 14% /mnt/storage
is the line you'll be looking at. see i've got 1.2gigs free
use
http://winscp.net/eng/download.php
to connect to the chumby scp port 22
put music on
/mnt/storage
as confirmation it does look on /mnt/storage for music. If you plug a usb drive in it will read from both the storage and usb drive. Mine was showing all songs but wouldn't play files on external drive, but after pressing eject and reopening the "my music files" it played from both