You should first check you can run telnet, maybe using JockyW customised firmware, or my post in this tread.
Once you have access to the telnet command, just mount your usb disk if it is not already mounted (check by using the mount command if it is there, otherwise type
then
Code:
mount /dev/scsi/host1/bus0/target0/lun0/part1 /tmp/usbdisk
to mount it. just browse the /dev/scsi folder to check if your usb device is under another name (host2 or 3 for example))
Once you have it mounted, just use the mv or cp command to place files on it: files should be in /tmp/usbdisk
You should then finish by a umount command to close the file system properly